Changelog

Python next

Release date: XXXX-XX-XX

Tools/Demos

  • gh-113318: Fix Argument Clinic for @getter and @setter in a preprocessor conditional block. It failed with an internal error. Argument Clinic now also rejects the accessors of the same attribute with different C basenames, and the same accessor defined twice, which silently generated invalid or duplicated entries of PyGetSetDef.

  • gh-64502: Fix Argument Clinic support of parameters with a default value used together with optional groups. Such parameters were always required in the generated parsing code.

Tests

  • gh-155411: Fix test.support.subTests() for asynchronous test methods. They were wrapped in a synchronous function, which discarded the coroutine without awaiting it, so the test silently did not run at all.

  • gh-132581: The list of tests which altered the execution environment now includes the reasons why the environment was considered altered, for example an unraisable exception or a modified sys.path. The final result no longer repeats the same state twice (like ENV CHANGED then ENV CHANGED).

Security

  • gh-155999: Fix the tarfile tar and data extraction filters creating directories outside the destination for members whose name leaves the destination and returns to it, such as ../evil/../dest/sub/file. The containment check used the resolved path, but intermediate directories were created from the name as given.

  • gh-155558: Update bundled libexpat to version 2.8.3 for the fix to CVE 2026-72522.

  • gh-155694: Fix CVE 2026-15806 by scoping HTTPPasswordMgr credentials to the URL scheme, preventing credentials stored for an HTTPS URL from being used for a matching HTTP URL, while URIs without a scheme continue to match any scheme.

Library

Core and Builtins

  • gh-129752: Don’t update adaptive counters in the free-threaded build when thread-local bytecode is disabled (-X tlbc=0). Patch by Donghee Na.

  • gh-155515: Track the internal HAMT iterators, which back iteration over a contextvars.Context, with the garbage collector. A reference cycle running through such an iterator was never collected, leaking the whole context it iterated over.

  • gh-154902: Fix a crash when __conditional_annotations__ is rebound to a non-set object.

  • gh-153578: Fix an out-of-bounds write in bytearray.extend() when the bytearray is resized while the argument’s __buffer__() is being acquired, for example by another thread. Patch by tonghuaroot.

  • gh-148817: Fold large constant list and set literals used as the iterable of a for loop or in/not in test into a constant tuple or frozenset, restoring an optimization previously done by the AST optimizer that was lost when constant folding moved to the CFG.

  • gh-85260: compile() now raises ValueError instead of crashing on a debug build if an identifier field of an AST node (such as the name of a function, a class, an imported module or a caught exception) is "None", "True" or "False".

Build

  • gh-155911: Fix curses detection when a curses library is already in LIBS. Patch by Shamil Abdulaev.

  • gh-156115: iOS simulator builds are now configured with -mios-simulator-version-min instead of the device’s -mios-version-min. The device flag made the linker reject libraries resolved from the simulator SDK, so library detection silently failed.

Python 3.14.7 final

Release date: 2026-08-05

Security

  • gh-153030: Fixed quadratic complexity in incremental parsing of long unterminated constructs (such as tags or comments) in html.parser.HTMLParser, which could be exploited for a denial of service.

  • gh-152674: The xml.etree.ElementTree.Element methods findall(), iterfind() and find() avoid quadratic behavior when using XPath index predicates ([1], [last()], [last()-N]) on XML documents with many same-tag siblings.

  • gh-152216: Update bundled libexpat to version 2.8.2.

  • gh-151987: The tarfile.TarFile.extract() method now applies the given filter when it extracts a link target from the archive as a fallback.

  • gh-151981: In tarfile, seeking a stream now stops when end of the stream is reached.

  • gh-151544: Modules/Setup.local is no longer used as a landmark to discover whether Python is running in a source tree, as it could potentially affect actual installs. The pybuilddir.txt file is now the sole indicator of running in a source tree.

  • gh-151558: Fixed an vulnerability in the tarfile data and tar extraction filters where crafted archives could create a symlink pointing outside the destination directory. This was a bypass of CVE 2025-4330.

  • gh-150743: http.client now limits the number of chunked-response trailer lines it will read to 100, and the number of interim (1xx) responses it will skip to 100. A malicious or broken server could previously stream trailer lines or 100 Continue responses forever, hanging the client even when a socket timeout was in use. Reported by @YLChen-007 via GHSA-w4q2-g22w-6fr4.

  • gh-143927: Normalize all line endings (CR, CRLF, and LF) to LF+TAB when writing multi-line configparser values.

  • gh-143921: Reject NUL, CR and LF characters in IMAP commands. Other control characters are allowed and sent quoted.

Core and Builtins

  • gh-133931: Fix data races when setting attributes of function objects on the free threaded build.

  • gh-154709: Fix an out-of-bounds access in reverse dictionary iterators when the underlying dictionary is cleared and modified after the iterator is created.

  • gh-154695: Fix asyncio.Task raising AttributeError when created with eager_start=True and no explicit loop argument.

  • gh-153809: Fix interpreter crash while deallocating objects of asyncio.Task on free-threaded builds. Contributed by Sergey Miryanov.

  • gh-154275: Fix a crash when getting deeply nested __parameters__ from a types.GenericAlias objects.

  • gh-153932: Fix thread safety issue in the __reduce__ method of enumerate.

  • gh-153298: Fixes a data race in types.GenericAlias __parameters__ initialization on free-threading builds.

  • gh-153205: Fix a potential SystemError during vector calls when memory allocation fails. A MemoryError is now raised instead.

  • gh-152682: Fix NULL pointer dereference in compile() when a reserved name (e.g. __classdict__) is used as a type parameter name and memory allocation fails while formatting the error message.

  • gh-152635: Fix a crash caused when running out of memory creating a _interpchannels channel. Now a MemoryError is correctly raised.

  • gh-152375: Fix undefined behaviour when a sys.monitoring callback raised an exception while the program was following a branch or loop.

  • gh-152235: Defer GC tracking of set.intersection(), set.difference(), set.symmetric_difference(), set.union() and set.__sub__. Patch by Donghee Na.

  • gh-152235: Defer GC tracking of a set or frozenset to the end of its construction from iterable. Patch by Donghee Na.

  • gh-152228: Fix an assertion failure when python is built in a debug mode that happened in str.replace() under a limited memory situation.

  • gh-151763: Fixes possible crash on types.CodeType deallocation.

  • gh-152020: On the free-threaded build, asyncio.all_tasks() no longer loses eager-started tasks when called from a thread other than the one running the event loop.

  • gh-151763: Fix a potential crash in compile(), exec(), eval() and ast.parse() when an allocation fails: the parser or compiler could return without setting an exception.

  • gh-151912: Fixed a crash in type() when selecting a metaclass whose tp_new slot is NULL. Such metaclasses are now rejected with TypeError instead of causing a NULL pointer dereference.

  • gh-151905: Fix OOM error handling in PyFrame_GetBack() to propagate exceptions instead of masking them as None.

  • gh-151773: Fix a crash in contextvars.ContextVar.set() when memory allocation fails.

  • gh-151126: Fix a crash when sharing memoryview objects between interpreters fails due to running out of memory. It now raises a proper MemoryError.

  • gh-151644: Fix a data race in sys.setdlopenflags() and sys.getdlopenflags() when called concurrently in the free-threaded build. The underlying _PyImport_GetDLOpenFlags and _PyImport_SetDLOpenFlags functions now use atomic load/store operations.

  • gh-151126: Avoid possible crash in _winapi.c where a device has no memory left. Now it properly raises a MemoryError. Patch by Ivy Xu.

  • gh-151546: Fix the stack limit check if Python is linked to musl (ex: Alpine Linux). Use the stack size set by the linker to compute the stack limits. Patch by Victor Stinner.

  • gh-151461: Fix direct execution of files with invalid source encodings to report the underlying codec lookup or decoding error instead of the generic SyntaxError: encoding problem message. Patch by Bartosz Sławecki.

  • gh-151218: PyConfig_Set() and sys.set_int_max_str_digits() now replace sys.flags (create a new object), instead of modifying sys.flags in-place. Patch by Victor Stinner.

  • gh-151253: If import encodings (first import) fails at Python startup, dump the Python path configuration to help users debugging their configuration. Patch by Victor Stinner.

  • gh-151238: Fix a crash when compiling a concatenated f-string or t-string if an error occurs when processing one of it’s parts.

  • gh-151126: Fix a crash, when there’s no memory left on a device, which happened in _interpchannels module.

    Now it raises proper MemoryError errors.

  • gh-150902: Apply an existing optimization of PyCriticalSection (single mutex) to PyCriticalSection2: avoid acquiring the same locks that the current CS has already acquired.

  • gh-151065: Fix memory leak when using the mimalloc memory allocator.

  • gh-151029: On Linux, fix sys.remote_exec() unable to find remote writable memory when libpython replaced on disk.

  • gh-150988: Fix a reference leak in OSError when attributes are set before super().__init__().

  • gh-144774: Fix data race in BaseException when an exception is copied while being mutated.

  • gh-150411: Fix a data race in the free-threaded build when gc.get_count() reads the young generation allocation count while another thread updates it.

  • gh-149689: Fix missing error propagation in parser action helpers when memory allocation fails. Patch by Thomas Kowalski.

  • gh-149162: Fix a potential deadlock in PyUnicode_InternFromString() and other interning functions in the free-threaded build when called from C++ static local initializers.

Library

  • gh-155009: Fix argparse.ArgumentParser to preserve the program name from sys.argv[0] when a named module is executed as the main program without replacing sys.argv[0].

  • gh-155063: Bump the version of pip bundled in ensurepip to version 26.2.1

  • gh-155063: Bump the version of pip bundled in ensurepip to version 26.2

  • gh-154936: Fix the pure Python json decoder to report the correct position for invalid literal control characters in JSON strings.

  • gh-154892: Fix a bug in the C accelerator for zoneinfo where datetime.datetime subclasses returning -1 for hour, minute, or second could incorrectly raise a SystemError.

  • gh-154848: The pickle C accelerator now enforces frame boundaries when unpickling, as the pure Python implementation already did. An argument that straddles a frame boundary, or a frame that begins before the previous one has ended, now raises pickle.UnpicklingError instead of being silently read across the boundary. This prevents the loaded data from diverging from the pickletools disassembly of the same pickle.

  • gh-109638: Fix exponential time in csv.Sniffer.sniff() for a sample which contains many quote characters. A doubled quote character is now also detected in a field which contains the delimiter or a line break.

  • gh-98820: Fix quadratic time in csv.Sniffer.sniff() for a sample which contains quoted fields, in particular for a single column of quoted fields.

  • gh-154738: Fix ExternalEntityParserCreate() not propagating the reparse-deferral setting to the subparser, which left GetReparseDeferralEnabled() returning an uninitialized value. Patch by tonghuaroot.

  • gh-93251: Fix UnicodeDecodeError in socket functions (such as getaddrinfo() and gethostbyaddr()) when the localized error message of the C library is not UTF-8: decode it from the locale encoding.

  • gh-154551: Fix ctypes.util.find_library() returning None in non-UTF-8 locales.

  • gh-79366: Fixed a race condition in logging: if a handler was removed while a record was being emitted, the following handlers of the same logger could be skipped.

  • gh-73458: Fix logging.config.listen(): it left the caller waiting for the ready event forever if the server could not be started, for example if the port was invalid or already in use. It now also binds to an IPv6 address if the host has no IPv4 address, for example if localhost is only aliased to ::1.

  • gh-154460: Fix time.strftime() and datetime.datetime.strftime() returning a wrong ISO 8601 week number (%V) on OpenBSD.

  • gh-154435: Fix os.posix_fadvise() and os.posix_fallocate() on DragonFly BSD: they raised OSError with a meaningless error code, because these functions return -1 and set errno there.

  • gh-154399: Fix venv activation in a non-interactive csh: activate.csh no longer fails when the prompt variable is not set.

  • gh-154389: Fix uuid.uuid1() on OpenBSD: it returned a version 4 UUID, because uuid_create() generates random UUIDs on this platform.

  • gh-154324: Fix os.sendfile() on illumos: it no longer reports a successful transfer when the underlying system call failed without writing any data.

  • gh-154307: Fix tempfile.TemporaryDirectory.cleanup() on DragonFly BSD, where removing a file with the UF_NOUNLINK flag failed with EISDIR instead of EPERM.

  • gh-154291: Fix socket.has_dualstack_ipv6() to return False on platforms such as DragonFly BSD where setting IPV6_V6ONLY to 0 silently has no effect.

  • gh-154283: On DragonFly BSD, threading.get_native_id() now returns a value that is unique across processes, matching the other platforms.

  • gh-154258: Fix a crash in mmap.mmap.resize() on NetBSD when growing a shared anonymous mapping. resize() now raises ValueError in this case, as it already did on Linux.

  • gh-131565: ctypes.util.dllist() now works on NetBSD. It is implemented in the _ctypes extension module so that dl_iterate_phdr() reports all loaded shared libraries: on NetBSD it only reports the link-map group of the calling object, which excluded them when called through ctypes.

  • gh-154225: Fix os.openpty() on Solaris and illumos: it no longer leaves the pseudo-terminal as the controlling terminal of the calling process.

  • gh-154227: Fix os.posix_openpt() on OpenBSD, where it rejected the O_CLOEXEC flag.

  • gh-145030: Fix asyncio write pipe transports for named FIFOs on macOS and Solaris. Unread data sitting in the FIFO made the transport misinterpret a poll event as the reader disconnecting, wrongly closing the transport.

  • gh-154001: Fix random.binomialvariate() raising ZeroDivisionError when random.random() returns zero.

  • gh-153908: Fix data race when calling repr() on itertools.count under the free-threaded build.

  • gh-153896: Deduplicate unhashable args in typing.Literal.

  • gh-153864: On a wide curses build, curses.window.insch() now inserts a non-ASCII byte as the character it encodes in the window’s encoding, consistently with addch(), instead of its code point.

  • gh-153862: On a wide curses build, curses.window.inch() now returns the locale-encoded byte of a non-ASCII character, matching instr(), instead of the low byte of its code point.

  • gh-146011: Fix a heap-use-after-free in the C implementation of decimal when calling repr() after deleting the Context.

  • gh-153761: Fix cancelling asyncio.loop.sock_accept() dropping a pending connection.

  • gh-153695: Hashing a sqlite3.Row that contains an unhashable value now raises TypeError instead of SystemError. Patch by tonghuaroot.

  • gh-127049: Fix a race condition in asyncio on Unix where asyncio.subprocess.Process.send_signal(), terminate() or kill() could signal an unrelated process that was recycled onto the PID of the already-reaped child when ThreadedChildWatcher is used. Patch by Kumar Aditya.

  • gh-153658: Fix sqlite3.Connection.iterdump() raising sqlite3.OperationalError when a table name contains a single quote. Patch by tonghuaroot.

  • gh-85943: Fix struct functions raising BytesWarning under the -bb command line option when a str format is used after an equal bytes format (or vice versa). The internal format cache no longer mixes str and bytes keys.

  • gh-153404: urllib.robotparser.RobotFileParser now silently ignores a Crawl-delay or Request-rate value written with non-decimal digits (such as U+00B2 SUPERSCRIPT TWO) instead of raising ValueError and aborting the parse of the whole robots.txt file.

  • gh-153417: Error messages from imaplib.IMAP4.select() and imaplib.IMAP4.uid() no longer raise BytesWarning under -bb when the mailbox or command argument is bytes.

  • gh-153406: email.utils.parsedate_to_datetime() now raises ValueError instead of OverflowError when the parsed year or timezone offset is out of range, matching its documented behavior.

  • gh-153083: Defer GC tracking of an array.array to the end of its construction. Patch by Donghee Na.

  • gh-153292: Fix data race in repr of threading.RLock in free-threading build.

  • gh-143990: A tkinter.font.Font created from a named font, including by copy(), now copies its configured options rather than the options resolved by Tcl’s font actual, preserving a size specified in pixels (a negative size).

  • gh-148286: Fix undefined behavior in compression.zstd.ZstdDecompressor.unused_data when a complete frame was decompressed in a single call.

  • gh-153210: Fix crash on array import under a memory pressure.

  • gh-153200: Fix math.isqrt() returning an incorrect result for arguments not less than 2**64 that are instances of an int subclass with an overridden comparison operator.

  • gh-153068: Fix cProfile.Profile.enable() to no longer overwrite errors from sys.monitoring.

  • gh-153062: Fix a crash when concurrently iterating an itertools.tee() iterator on the free-threaded build.

  • gh-153056: Fix string.Template raising a spurious ValueError when the pattern attribute is a compiled regular expression object, which the documentation allows. On the free-threaded build this also occurred as a data race on the first concurrent use.

  • gh-153037: Fix ZstdFile raising AttributeError instead of io.UnsupportedOperation when iterating over a file that is not open for reading.

  • gh-135661: Fix html.parser.HTMLParser: an abruptly closed empty comment (<!--> or <!--->) no longer extends up to a later --> in the same feed() call.

  • gh-152851: Prevent a crash when allocation fails while copying a BLAKE-2s/2b object. Patch by Bénédikt Tran.

  • gh-54930: Error responses of http.server.BaseHTTPRequestHandler to malformed request lines now include a status line and headers instead of being sent in the bare HTTP/0.9 style. Only a valid HTTP/0.9 request (a two-word GET request line) now receives an HTTP/0.9 style response.

  • gh-119592: Fix concurrent.futures.ProcessPoolExecutor stranding submitted work forever when a worker process exited upon reaching its max_tasks_per_child limit after shutdown() was called with wait=False: a replacement worker is now spawned and the remaining work executed as documented. If the executor has instead been garbage collected without shutdown() (gh-152967), or a replacement worker cannot be started, the remaining futures now fail with BrokenProcessPool instead of never resolving. A worker exit racing shutdown(wait=False) can also no longer crash the executor management thread.

  • gh-152951: collections.deque prevent rare crash when calling extend under high memory pressure conditions.

  • gh-150880: Normalize non-extended Windows paths before appending the wildcard used by os.listdir() and os.scandir(), making paths with trailing spaces behave consistently with other filesystem APIs.

  • gh-152849: Out-of-range float and integer timestamps now raise OverflowError with the same message. Patch by tonghuaroot.

  • gh-152847: Reject a POSIX TZ transition rule with non-digit characters in the day-of-year field in the pure-Python zoneinfo parser. Patch by tonghuaroot.

  • gh-108280: Connecting imaplib to a server that does not send a valid IMAP4 greeting (for example a POP3 server answering on the IMAP port) now raises an error reporting the server’s response instead of imaplib.IMAP4.error: None.

  • gh-63121: imaplib now refreshes the cached capability list after a successful login() or authenticate(), using the CAPABILITY response sent by the server or, if none was sent, by querying it, so that capabilities that become available only after authentication (such as ENABLE on Gmail) are recognized. Capabilities advertised in the server greeting are now also used, avoiding a redundant CAPABILITY command.

  • gh-88574: imaplib no longer fails when a server sends a spurious blank line after the counted data of a literal, including after a literal that terminates a response (such as a mailbox name returned by LIST). Such blank lines are now skipped without swallowing the following line.

  • gh-152502: Detect the curses mouse interface (getmouse(), the BUTTON* constants, and others) with a configure capability probe or library macros instead of gating it on ncurses-specific macros. It is now also available with other curses implementations that provide it, such as NetBSD curses and PDCurses (the latter underpins windows-curses).

  • gh-151842: Fix a crash in _interpreters.capture_exception() when MemoryError happens. Patch by Amrutha Modela.

  • gh-40038: imaplib now again quotes command arguments when necessary, for example mailbox names containing a space. Such quoting was inadvertently disabled when the module was ported to Python 3, and the arguments are now quoted according to the RFC 3501 grammar. For backward compatibility, an argument already enclosed in double quotes is left unchanged, so code that quotes arguments itself keeps working.

  • gh-50966: Fix unbounded recursion in turtle when a mouse event handler that moves the turtle is reentered while the screen is being redrawn, for example with screen.ondrag(turtle.goto). This could previously crash the interpreter.

  • gh-152569: Fix asyncio.wait() leaking waiting tasks via the await-graph when racing a future that never resolves. The waiting task is now discarded from every future’s awaited_by set once wait() returns, even for pending futures.

  • gh-78335: Update the docstrings of tkinter and tkinter.ttk widget classes to list all supported widget options, including options added in Tk 9.0 and 9.1. tkinter.Menubutton and tkinter.Message previously had no option list at all.

  • gh-152431: Fix asyncio.StreamWriter.start_tls() to keep the linked StreamReader transport in sync with the upgraded transport.

  • gh-151126: Fix two crashes in tkinter and socket modules initialization under a memory pressure. Sets missing MemoryError.

  • gh-133031: curses.textpad.Textbox now enters and reads back the non-ASCII characters of an 8-bit locale encoding, instead of mangling them with a 7-bit mask.

  • gh-71880: curses.textpad.Textbox now lets the lower-right cell of the window be edited. Writing it with addch() would move the cursor past the end of the window, raising an error and scrolling a scrollable window, so it is now written with insch(), which keeps the cursor in place.

  • gh-83274: Deallocating a tkinter application from a thread other than the one it was created in no longer crashes the interpreter. The underlying Tcl interpreter is leaked instead, and a RuntimeWarning is reported.

  • gh-152305: Fix the pure-Python datetime.time.strftime() implementation raising AttributeError for the year directives. Patch by tonghuaroot.

  • gh-88758: tkinter.Misc.focus_get(), focus_displayof(), focus_lastfor() and winfo_containing() now return None instead of raising KeyError when the widget was not created by tkinter (for example a torn-off menu).

  • gh-38464: tkinter.Misc.nametowidget() now resolves the auto-generated names of cloned menus (a menu used as a menubar or a cascade) back to the original widget.

  • gh-152248: Make the C and pure-Python zoneinfo parsers validate POSIX TZ abbreviations consistently, rejecting unquoted abbreviations with non-letter characters and empty quoted abbreviations. Patch by tonghuaroot.

  • gh-80937: Fix a memory leak in tkinter when a Tcl command created with createcommand was not explicitly removed before the interpreter was deleted. The command no longer keeps the interpreter alive through a reference cycle.

  • gh-152246: Fix the pure-Python zoneinfo parser accepting an invalid POSIX TZ transition rule with a non-period separator. Patch by tonghuaroot.

  • gh-139816: Fix a hang in tkinter on interactive Python built without readline. An exception raised in a callback no longer causes the event loop to stop and wait for the user to press Enter; pending callbacks now keep running until input is actually available on stdin.

  • gh-139145: Fix a busy loop in tkinter on interactive Python. When a Tcl command running its own event loop (such as vwait or wait_variable()) was active and input arrived on stdin, the event loop kept spinning at 100% CPU. The stdin file handler is now removed as soon as input is available. Based on a patch by Michiel de Hoon.

  • gh-152212: Fix the pure-Python zoneinfo parser accepting a POSIX TZ string with a std abbreviation but no offset. This is invalid per POSIX and now raises ValueError, matching the C accelerator. Patch by tonghuaroot.

  • gh-152156: Fix a possible crash in concurrent.interpreters.create() under limited memory conditions.

  • gh-152157: The C implementations of fromisoformat() and fromisoformat() now reject a decimal separator that is not followed by any fractional digit before a timezone designator.

  • gh-151763: Fix crash in _interpqueues.create() whe MemoryError happens on queue creation.

  • gh-105895: Add match and case to the list of supported topics by help().

  • gh-152079: Fix datetime.datetime.fromisoformat() in the C implementation dropping the sub-second part of a UTC offset whose whole-second part is zero, matching the pure-Python implementation.

  • gh-152052: The json C accelerator now correctly reports an unterminated string for a \uXXXX escape at the end of the input.

  • gh-152060: Fix datetime.datetime.fromisoformat() raising AssertionError instead of ValueError for some malformed strings in the pure-Python implementation, matching the C implementation.

  • gh-126219: Fixed a crash in tkinter.Tk when className contains a non-BMP character and tkinter is built against Tcl/Tk 8.x. Such a name is now rejected with a ValueError.

  • gh-86165: Fix imaplib.Time2Internaldate() to use the local timezone offset for time.struct_time values with tm_gmtoff set to None, as returned by datetime.datetime.timetuple(). Contributed by Xiao Yuan.

  • gh-151814: Fix unbounded memory growth in io.TextIOWrapper when repeatedly writing an empty string.

  • gh-151770: Fix datetime.datetime.fromisoformat() raising AssertionError instead of ValueError for an out-of-range month combined with a 24:00 time.

  • gh-151665: inspect.signature() now works on the lazy evaluators of type aliases and type parameters instead of raising ValueError.

  • gh-151695: Fix a use-after-free in the curses module. The encoding of the initial screen, used by curses.unctrl() and curses.ungetch() to encode non-ASCII characters, is now kept as a private copy instead of a borrowed pointer to a window object that may be deallocated.

  • gh-151596: Add missing size positional argument to the pure-Python implementation of io.TextIOBase.readline().

  • gh-151640: Fix a data race in io.BytesIO in free-threaded builds when whole-buffer reads or peeks, or getvalue(), share the internal buffer with concurrent writes.

  • gh-148660: Fix a crash in collections.OrderedDict.copy() when a key’s __eq__ or a subclass method mutates the dict during the copy. Now raises RuntimeError instead, as iteration does.

  • gh-151497: Opening a tarfile archive no longer attempts to pre-allocate a huge buffer when a crafted or truncated member claims an oversized extended header (a GNU long name/link or a pax header). The extended header is now read in bounded chunks, so its size field can no longer trigger memory exhaustion.

  • gh-151403: Fixed a crash in subprocess.Popen (and _posixsubprocess.fork_exec) when an argv item’s __fspath__() concurrently mutates the args sequence being converted.

  • gh-151390: Colorize match in the REPL when followed by a unary + or - operator. Patch by Bartosz Sławecki.

  • gh-151126: Fix crash on unset MemoryError on allocation failure in ctypes.get_errno().

  • gh-151416: Fix a crash in os.spawnv() and os.spawnve() when an argv item’s __fspath__() method mutates the argv list during argument conversion. os.spawnv() argument conversion errors other than TypeError, such as the ValueError for an embedded null, are no longer replaced with a generic TypeError.

  • gh-151337: Avoid possible memory leak in tkinter.c on Windows.

  • gh-151126: Fix a crash when MemoryError in os._path_splitroot() was not set properly.

  • gh-151126: Fix a crash, when there’s no memory left on a device, which happened in _interpchannels module.

    Now it raises proper MemoryError errors.

  • gh-119710: Fix asyncio subprocess wait() hanging when the process has exited but one of its pipes is kept open by an inherited child process (so the pipe never reaches EOF). wait() now returns as soon as the process exits, regardless of the pipes’ state.

  • gh-151295: Fixed a crash (use-after-free) in bytes.join() and bytearray.join() that could occur if an item’s __buffer__() concurrently mutates the sequence being joined. The mutation is now reported as a RuntimeError instead.

  • gh-109940: Fix Windows venv activation in cmd.exe to respect VIRTUAL_ENV_DISABLE_PROMPT.

  • gh-117807: Fix mimetypes initialization from MIME map files containing invalid UTF-8 bytes.

  • gh-150583: Correctly set the default compression level in compression.zstd when passing a digested dictionary during compression.

  • gh-150641: Fix bug where typing.evaluate_forward_ref() with the STRING format could leak internal names used by the annotation machinery.

  • gh-150484: Fix unittest.mock.mock_open() __exit__ raising TypeError when used with contextlib.ExitStack.

  • gh-149816: Fix a potential use after free condition in pickle.dumps() in free-threaded mode when serializing lists.

  • gh-149319: The asyncio REPL now ignores PYTHONSTARTUP and PYTHON_BASIC_REPL when -E or -I is used. Patch by Jonathan Dung.

  • gh-47005: Fix urllib.request.AbstractHTTPHandler.do_open() to give regular headers set via add_header() priority over unredirected headers, consistent with get_header() and header_items().

  • gh-123471: Make concurrent iteration over itertools.zip_longest safe under free-threading.

  • gh-123720: asyncio: Fix asyncio.Server.serve_forever() shutdown regression. Since 3.12, cancelling serve_forever() could hang waiting for a handler blocked on a read from a client that never closed (effectively requiring two interrupts to stop); the shutdown sequence now ensures client streams are closed so serve_forever() exits promptly and handlers observe EOF.

  • gh-123471: Make concurrent iteration over itertools.accumulate safe under free-threading.

  • gh-123471: Make concurrent iteration over itertools.combinations_with_replacement and itertools.permutations safe under free-threading.

  • gh-143988: Fixed crashes in socket.socket.sendmsg() and socket.socket.recvmsg_into() that could occur if buffer sequences are concurrently mutated.

  • gh-130796: Undeprecate the locale.getdefaultlocale() function. Patch by Victor Stinner.

  • gh-115634: Fix a deadlock in concurrent.futures.ProcessPoolExecutor when using max_tasks_per_child, present since the feature was introduced in Python 3.11. The executor stopped scheduling queued tasks after a worker process exited upon reaching its task limit. Based on a fix proposed by Tabrez Mohammed.

  • gh-140326: Fix the asyncio REPL namespace so that relative imports no longer resolve against the asyncio package and __file__ is no longer set.

  • gh-79638: Disallow all access in urllib.robotparser if the robots.txt file is unreachable due to server or network errors.

  • gh-123471: Make concurrent iterations over itertools.chain safe under free threading.

  • gh-123471: Make concurrent iterations over itertools.combinations and itertools.product safe under free-threading.

  • gh-123471: Make concurrent iterations over itertools.cycle safe under free-threading.

  • gh-120665: Fixed an issue where unittest loaders would load and instantiate unittest.TestCase-derived subclasses that are also abstract base classes, which can’t be instantiated.

  • gh-105708: Accept an uppercase V prefix in IPvFuture addresses in urllib.parse.urlsplit().

  • gh-103925: Fix csv.Sniffer.sniff() for a sample with \r\n line endings in which a quoted field ends a line: a letter could be detected as the delimiter.

  • gh-101267: When a worker process terminates unexpectedly, concurrent.futures.ProcessPoolExecutor now sets a separate BrokenProcessPool exception on each pending future instead of sharing a single instance among them all. Sharing one exception produced malformed tracebacks: each Future.result() call re-raised the same object, appending another copy of the traceback to it.

Documentation

  • gh-118150: Clarify in the difflib documentation what junk actually does, its drawbacks, and how to control it.

  • gh-86726: Greatly expand the tkinter documentation to cover the full public API of the package and its submodules. The descriptions are oriented towards Python rather than Tcl/Tk, with corrected return types and versionadded/versionchanged information.

Tests

  • gh-155109: Add test.support.run_with_limited_c_stack() and use it in tests that exhaust the C stack with a fixed number of recursive calls, so that their outcome no longer depends on the C stack size.

  • gh-76595: Add C API tests for PyCapsule_Import().

  • gh-154211: Add test.support.skip_if_huge_c_stack() and use it to skip tests that exhaust the C stack if the stack limit is very large (e.g. on DragonFly BSD or with ulimit -s unlimited).

  • gh-154167: The test runner (regrtest) now restores the default SIGINT handler if it was inherited as ignored, so the test suite no longer hangs when run as a shell background job.

  • gh-154144: Fix building the _testcapi module on NetBSD.

  • gh-152548: Add the test.support.isolation.runInSubprocess() decorator to run a test method or TestCase subclass in a fresh interpreter subprocess, isolated from the rest of the test run.

  • gh-151626: Fix several tests in test.test_inspect, test.test_import, test.test_importlib, test.test_py_compile and test.test_compileall that failed when the test suite was run with PYTHONPYCACHEPREFIX set. These tests now neutralize the pycache prefix where they assume the default __pycache__ bytecode layout.

  • gh-151096: Fix test_embed failing when CPython is configured with a split exec prefix (--exec-prefix differing from --prefix).

  • gh-148853: Fix tests failing on FreeBSD in test.support’s in_systemd_nspawn_sync_suppressed() due to unreadable /run directory.

Build

  • gh-154070: Build the curses module against a wide-character capable ncurses even when it is not named ncursesw – for example the pkgsrc ncurses on NetBSD and illumos, or the system ncurses on macOS. Such a library previously produced a narrow build.

  • gh-126877: Fix the configure check for Tcl/Tk which could wrongly succeed with optimizing compilers when the libraries are missing.

  • gh-153438: Update Windows build and installer tooling and documentation to use the current download URL for nuget.exe.

  • gh-152502: The curses module now detects set_escdelay(), set_tabsize() and the ESCDELAY and TABSIZE variables with configure capability probes instead of the ncurses-specific NCURSES_EXT_FUNCS macro, so they are exposed when building against other curses implementations such as NetBSD curses that provide them.

  • gh-148260: On Linux when Python is linked to the musl C library, use a thread stack size of at least 1 MiB instead of musl default which is 128 kiB. Patch by Victor Stinner.

  • gh-138800: Fix library name in python3.pc on Android.

Windows

  • gh-124111: Updated Windows builds to use Tcl/Tk 9.0.4.

  • gh-150836: Make installed tkinter work with Tcl/Tk 9 builds that embed the Tk script library in the Tk DLL on Windows.

  • gh-140146: Prevent tkinter from hanging on Windows if stdin is redirected to a pipe in an interactive session. This is helpful for testing interactive usage of tkinter from a script, for example as part of the cpython test suite.

macOS

  • gh-153711: On macOS, do not attempt to use the dup3(2) and pipe2(2) system calls introduced in macOS 27 to prevent problems when running on older systems.

  • gh-124111: Update macOS installer to use Tcl/Tk 9.0.4.

IDLE

  • gh-82183: When the shell is busy running code, using “Run… Customized” with “Restart shell” unchecked now reports that the shell is executing instead of restarting it anyway.

  • gh-83653: Blanking an integer entry in IDLE’s Settings dialog, such as “Auto squeeze min lines”, no longer saves an empty string as an invalid configuration value.

  • gh-65339: Saving the IDLE Shell or an Output window now defaults to a .txt extension and lists text files before Python files, since their content is not Python source.

  • gh-80504: The “In files:” field of IDLE’s Find in Files dialog now always contains a full directory path, even for an unsaved editor or the Shell. This shows in the grep output which directory was searched.

  • gh-134300: Do not add the idlelib directory to the path of the IDLE user process. User code run in IDLE can no longer import idlelib submodules as top-level modules, such as import help.

  • gh-89360: Fix a rare crash in the IDLE editor when the completion window is closed: deleting a key binding for a sequence that is not bound to the virtual event is now ignored instead of raising a ValueError.

  • gh-71956: Fix Replace All in the IDLE editor’s Replace dialog when the search direction is “Up” and “Wrap around” is off: it now replaces all matches above the current position instead of only the first one.

  • gh-152728: Move functions run.fix_scaling, editor.fixwordbreaks (as fix_word_breaks) and pyshell.fix_x11_paste to idlelib.util.

  • gh-66331: Set the WM_CLASS window property of IDLE’s windows to Idle on X11, so that window managers group and label them correctly instead of using the default Toplevel.

  • gh-85320: IDLE now reads and writes its configuration files and the breakpoints file using UTF-8 instead of the locale encoding. This keeps non-ASCII data (such as non-ASCII paths) from being corrupted and makes the files portable between environments.

  • gh-94523: Detect file if modified at local disk and prompt to ask refresh. Patch by Shixian Li.

  • gh-139551: Support rendering BaseExceptionGroup in IDLE.

  • gh-89520: Make IDLE extension configuration look at user config files, allowing user-installed extensions to have settings and key bindings defined in ~/.idlerc.

Tools/Demos

  • gh-155218: Fix Argument Clinic generating the flags of the optional groups in different order on 32-bit and 64-bit platforms.

  • gh-155207: Argument Clinic now supports the --dry-run and --diff options. They list the files which would be changed, or write a unified diff of the changes to the standard output, without modifying any file.

  • gh-154580: Fix python-gdb.py raising UnicodeEncodeError when pretty-printing a non-ASCII str in a locale whose host charset cannot encode it, such as any non-ASCII string in the C locale.

C API

Python 3.14.6 final

Release date: 2026-06-10

Security

  • gh-151159: Update Android and iOS installers to use OpenSSL 3.5.7.

  • gh-150599: Fix a possible stack buffer overflow in bz2 when a bz2.BZ2Decompressor is reused after a decompression error. The decompressor now becomes unusable after libbz2 reports an error.

  • gh-149835: shutil.move() now resolves symlinks via os.path.realpath() when checking whether the destination is inside the source directory, preventing a symlink-based bypass of that guard.

  • gh-149698: Update bundled libexpat to version 2.8.1 for the fix for CVE 2026-45186.

  • gh-87451: The ftplib module’s undocumented ftpcp function no longer trusts the IPv4 address value returned from the source server in response to the PASV command by default, completing the fix for CVE-2021-4189. As with ftplib.FTP, the former behavior can be re-enabled by setting the trust_server_pasv_ipv4_address attribute on the source ftplib.FTP instance to True. Thanks to Qi Deng at Aurascape AI for the report.

  • gh-149486: tarfile.data_filter() now validates link targets using the same normalised value that is written to disk, strips trailing separators from the member name when resolving a symlink’s directory, and rejects link members that would replace the destination directory itself. This closes several path-traversal bypasses of the data extraction filter.

  • gh-149079: Fix a potential denial of service in unicodedata.normalize(). The canonical ordering step of Unicode normalization used a quadratic-time insertion sort for reordering combining characters, which could be exploited with crafted input containing many combining characters in non-canonical order. Replaced with a linear-time counting sort for long runs.

  • gh-149018: Improved protection against XML hash-flooding attacks in xml.parsers.expat and xml.etree.ElementTree when Python is compiled with libExpat 2.8.0 or later.

Core and Builtins

  • gh-151112: Fix a crash in the compiler that could occur when running out of memory.

  • gh-151126: Fix a crash, when there’s no memory left on a device, which happened in:

    • code compilation - _winapi.CreateProcess()

    Now these places raise proper MemoryError errors.

  • gh-150700: Fix a SystemError when compiling a class-scope comprehension containing a lambda that references __class__, __classdict__, or __conditional_annotations__. Patch by Bartosz Sławecki.

  • gh-150633: Fix the frozen importer accepting module names with embedded null bytes, which caused it to bypass the sys.modules cache and create duplicate module objects.

  • gh-148613: Fix a data race in the free-threaded build between gc.set_threshold() and garbage collection scheduling during object allocation.

  • gh-149156: Fix an intermittent crash after os.fork() when perf trampoline profiling is enabled and the child returns through trampoline frames inherited from the parent process.

  • gh-149449: Fix a use-after-free crash when the unicodedata module was removed from sys.modules and garbage-collected between calls that decode \N{...} escapes or use the namereplace codec error handler.

  • gh-150207: Fix a crash when a memory allocation fails during tokenizer initialization. A proper MemoryError is now raised instead.

  • gh-150107: asyncio: sendfile() and sock_sendfile() event loop methods now call file.seek(offset) if file has a seek() method, even if offset is 0 (default value).

  • gh-150146: Fix a crash on a complex type variable substitution.

    from typing import TypeVar; memoryview[TypeVar("")][*typing.Mapping[..., ...]] used to fail due to missing NULL check on _unpack_args C function call.

  • gh-149590: Fix crash when faulthandler is imported more than once.

  • gh-149816: Fix a race condition in _PyBytes_FromList in free-threading mode.

  • gh-149816: Fix a race condition in memoryview with free-threading.

  • gh-149805: Fix a SystemError when compiling a compiling __classdict__ class annotation. Found by OSS-Fuzz in #512907042.

  • gh-149738: sqlite3: Disallow removing row_factory and text_factory attributes of a connection to prevent a crash on a query.

  • gh-139808: Add branch protections for AArch64 (BTI/PAC) in assembly code used by -X perf_jit (Linux perf profiler integration).

  • gh-148450: Fix abc.register() so it invalidates type version tags for registered classes.

Library

  • gh-151039: Fix a crash when static datetime types outlive the _datetime module.

  • gh-150913: Fix sqlite3.Blob slice assignment to raise TypeError and IndexError for type and size mismatches respectively, even when the target slice is empty.

  • gh-143008: Fix race conditions when re-initializing a io.TextIOWrapper object.

  • gh-150750: Fix a race condition in collections.deque.index() with free-threading.

  • gh-150685: Update bundled pip to 26.1.2

  • gh-150406: Fix a possible crash occurring during socket module initialization when the system is out of memory on platforms without a reentrant gethostbyname.

  • gh-150372: readline: Fix a potential crash during tab completion caused by an out-of-memory error during module initialization.

  • gh-150157: Fix a crash in free-threaded builds that occurs when pickling by name objects without a __module__ attribute while sys.modules is concurrently being modified.

  • gh-150175: Fix race condition in unittest.mock.ThreadingMock where concurrent calls could lose increments to call_count and other attributes due to a missing lock in _increment_mock_call.

  • gh-84353: Preserve non-UTF-8 encoded filenames when appending to a zipfile.ZipFile. Previously, non-ASCII names stored in a legacy encoding (without the UTF-8 flag bit set) could be corrupted when the central directory was rewritten: they were decoded as cp437 and then re-stored as UTF-8.

  • gh-149816: Fix race condition in ssl.SSLContext.sni_callback

  • gh-149995: Update various docstrings in typing.

  • gh-88726: The email package now uses standard MIME charset names “gb2312” and “big5” instead of non-standard names “eucgb2312_cn” and “big5_tw”.

  • gh-149571: Fix the C implementation of xml.etree.ElementTree.Element.itertext(): it no longer emits text for comments and processing instructions.

  • gh-149921: Fix reference leaks in error paths of the _interpchannels and _interpqueues extension modules.

  • gh-149816: Fix a race condition in _random.Random.__init__ method in free-threading mode.

  • gh-149801: Add IANA registered names and aliases with leading zeros before number (like IBM00858, CP00858, IBM01140, CP01140) for corresponding codecs.

  • gh-149701: Fix bad return code from Lib/venv/bin/activate if hashing is disabled

  • gh-112821: In the REPL, autocompletion might run arbitrary code in the getter of a descriptor. If that getter raised an exception, autocompletion would fail to present any options for the entire object. Autocompletion now works as expected for these objects.

  • gh-149489: Fix ElementTree serialization to HTML. The content of elements “xmp”, “iframe”, “noembed”, “noframes”, and “plaintext” is no longer escaped. The “plaintext” element no longer have the closing tag.

  • gh-149231: In tomllib, the number of parts in TOML keys is now limited.

  • gh-149046: io: Fix io.StringIO serialization: no longer call str(obj) on str subclasses. Patch by Thomas Kowalski.

  • gh-148954: Fix XML injection vulnerability in xmlrpc.client.dumps() where the methodname was not being escaped before interpolation into the XML body.

  • gh-148441: xml.parsers.expat: prevent a crash in CharacterDataHandler() when the character data size exceeds the parser’s buffer size.

  • gh-146452: Fix segfault in pickle when pickling a dictionary concurrently mutated by another thread in the free-threaded build.

  • gh-142831: Fix a crash in the json module where a use-after-free could occur if the object being encoded is modified during serialization.

  • gh-90949: Add SetBillionLaughsAttackProtectionActivationThreshold() and SetBillionLaughsAttackProtectionMaximumAmplification() to xmlparser objects to tune protections against billion laughs attacks. Patch by Bénédikt Tran.

  • gh-134261: zip: On reproducible builds, ZipFile uses UTC instead of the local time when writing file datetimes to avoid underflows.

  • gh-128110: Fix bug in the parsing of email address headers that could result in extraneous spaces in the decoded text when using a modern email policy. Space between pairs of adjacent RFC 2047 encoded-words is now ignored, per section 6.2 (and consistent with existing parsing of unstructured headers like Subject).

  • gh-107398: Fix tarfile stream mode exception when process the file with the gzip extra field.

  • gh-123853: Update the table of Windows language code identifiers (LCIDs) used by locale.getdefaultlocale() on Windows to protocol version 16.0 (2024-04-23).

  • gh-91099: imaplib.IMAP4.login() now raises exceptions with str instead of bytes. Patch by Florian Best.

Documentation

  • gh-150319: Generic builtin and standard library types now document the meaning of their type parameters.

  • gh-109503: Fix documentation for shutil.move() on usage of os.rename() since nonatomic move might be used even if the files are on the same filesystem. Patch by Fang Li

Tests

  • gh-151130: Add more tests for PyWeakref_* C API.

  • gh-149776: Fix test_socket on Linux kernel 7.1 and newer: skip UDP Lite tests if it’s not supported. Patch by Victor Stinner.

Build

  • gh-148294: Corrected the use of AC_PATH_TOOL in configure.ac to allow a C++ compiler to be found on PATH.

Windows

  • gh-151159: Updated bundled version of OpenSSL to 3.5.7.

macOS

  • gh-151159: Update macOS installer to use OpenSSL 3.5.7.

  • gh-150644: When system logging is enabled (with config.use_system_logger, messages are now tagged as public. This allows the macOS 26 system logger to view messages without special configuration.

  • gh-115119: Update macOS installer to use libmpdecimal 4.0.1.

IDLE

  • bpo-6699: Warn the user if a file will be overwritten when saving.

C API

Python 3.14.5 final

Release date: 2026-05-10

Security

  • gh-148178: Hardened _remote_debugging by validating remote debug offset tables before using them to size memory reads or interpret remote layouts.

Core and Builtins

Library

Tests

  • gh-149425: Increase time delta in test.test_zipfile.test_core.OtherTests.test_write_without_source_date_epoch

  • gh-145736: Fix test_tkinter test_configure_values test case backport miss for Tk 9.

macOS

  • gh-142295: For Python macOS framework builds, update Info.plist files to be more compliant with current Apple guidelines. Original patch contributed by Martinus Verburg.

  • gh-124111: Update macOS installer to use Tcl/Tk 9.0.3.

Python 3.14.5 release candidate 1

Release date: 2026-05-04

Security

  • gh-149254: Update Android and iOS installer to use OpenSSL 3.0.20.

  • gh-149017: Update bundled libexpat to version 2.8.0.

  • gh-90309: Base64-encode values when embedding cookies to JavaScript using the http.cookies.BaseCookie.js_output() method to avoid injection and escaping.

  • gh-148808: Added buffer boundary check when using nbytes parameter with asyncio.AbstractEventLoop.sock_recvfrom_into(). Only relevant for Windows and the asyncio.ProactorEventLoop.

  • gh-148395: Fix a dangling input pointer in lzma.LZMADecompressor, bz2.BZ2Decompressor, and internal zlib._ZlibDecompressor when memory allocation fails with MemoryError, which could let a subsequent decompress() call read or write through a stale pointer to the already-released caller buffer.

  • gh-148169: A bypass in webbrowser allowed URLs prefixed with %action to pass the dash-prefix safety check.

  • gh-146581: Fix vulnerability in shutil.unpack_archive() for ZIP files on Windows which allowed to write files outside of the destination tree if the patch in the archive contains a Windows drive prefix. Now such invalid paths will be skipped. Files containing “..” in the name (like “foo..bar”) are no longer skipped.

  • gh-146333: Fix quadratic backtracking in configparser.RawConfigParser option parsing regexes (OPTCRE and OPTCRE_NV). A crafted configuration line with many whitespace characters could cause excessive CPU usage.

  • gh-146211: Reject CR/LF characters in tunnel request headers for the HTTPConnection.set_tunnel() method.

Core and Builtins

  • gh-149122: Fix a crash in optimized calls to all(), any(), tuple(), list(), and set() with an async generator expression argument (for example, tuple(await x for x in y)). These calls now correctly raise TypeError instead of crashing.

  • gh-113956: Fix a data race in sys.intern() in the free-threaded build when interning a string owned by another thread. An interned copy owned by the current thread is used instead when it is not safe to immortalize the original.

  • gh-148820: Fix a race in _PyRawMutex on the free-threaded build where a Py_PARK_INTR return from _PySemaphore_Wait could let the waiter destroy its semaphore before the unlocking thread’s _PySemaphore_Wakeup completed, causing a fatal ReleaseSemaphore error.

  • gh-148653: Forbid marshalling recursive code objects and slice objects which cannot be correctly unmarshalled.

  • gh-142516: Forward-port the generational cycle garbage collector to the default 3.14 build, replacing the incremental collector while leaving the free-threaded collector unchanged.

  • gh-148390: Fix an undefined behavior in memoryview when using the native boolean format (?) in cast(). Previously, on some common platforms, calling memoryview(b).cast("?").tolist() incorrectly returned [False] instead of [True] for any even byte b. Patch by Bénédikt Tran.

  • gh-148418: Fix a possible reference leak in a corrupted TYPE_CODE marshal stream.

  • gh-148393: Fix data races between PyDict_Watch() / PyDict_Unwatch() and concurrent dict mutation in the free-threaded build.

  • gh-148284: Fix high stack consumption in Python’s interpreter loop on Clang 22 by setting function limits for inlining when building with computed gotos.

  • gh-148037: Remove critical section from PyCode_Addr2Line() in free-threading.

  • gh-148222: Fix vectorcall support in types.GenericAlias when the underlying type does not support the vectorcall protocol. Fix possible leaks in types.GenericAlias and types.UnionType in case of memory error.

  • gh-148208: Fix recursion depth leak in PyObject_Print()

  • gh-137814: Fix the __qualname__ attribute of __annotate__ functions on functions.

  • gh-147998: Fixed a memory leak in interpreter helper calls so cleanup works when an operation falls across interpreter boundaries. Patch by Maurycy Pawłowski-Wieroński.

  • gh-146455: Fix O(N²) compile-time regression in constant folding after it was moved from AST to CFG optimizer.

Library

  • gh-149221: Catch rare math domain error for random.binomialvariate().

  • gh-149117: Fix runpy.run_module() and runpy.run_path() to set the name attribute on the ImportError they raise.

  • gh-149148: ensurepip: Upgrade bundled pip to 26.1. This version fixes the CVE 2026-3219 vulnerability. Patch by Victor Stinner.

  • gh-148093: Fix an out-of-bounds read of one byte in binascii.a2b_uu(). Raise binascii.Error, instead of reading past the buffer end.

  • gh-148914: Fix memoization of in-band PickleBuffer in the Python implementation of pickle. Previously, identical PickleBuffers did not preserve identity, and empty writable PickleBuffer memoized an empty bytearray object in place of b'', so the following references to b'' were unpickled as an empty bytearray object.

  • gh-148947: Fix crash in @dataclasses.dataclass with slots=True that occurred when a function found within the class had an empty __class__ cell.

  • gh-148680: ForwardRef objects that contain internal names to represent known objects now show the type_repr of the known object rather than the internal __annotationlib_name_x__ name when evaluated as strings.

  • gh-148801: xml.etree.ElementTree: Fix a crash in Element.__deepcopy__ on deeply nested trees.

  • gh-148735: xml.etree.ElementTree: Fix a use-after-free in Element.findtext when the element tree is mutated concurrently during the search.

  • gh-148740: Fix usage for uuid command-line interface to support a custom namespace be provided for uuid3 and uuid5.

  • gh-148651: Fix reference leak in compression.zstd.ZstdDecompressor when an invalid option key is passed.

  • gh-146553: Fix infinite loop in typing.get_type_hints() when __wrapped__ forms a cycle. Patch by Shamil Abdulaev.

  • gh-148508: An intermittent timing error when running SSL tests on iOS has been resolved.

  • gh-148518: If an email containing an address header that ended in an open double quote was parsed with a non-compat32 policy, accessing the username attribute of the mailbox accessed through that header object would result in an IndexError. It now correctly returns an empty string as the result.

  • gh-148464: Add missing __ctype_le/be__ attributes for c_float_complex and c_double_complex. Patch by Sergey B Kirpichev.

  • gh-148370: configparser: prevent quadratic behavior when a ParsingError is raised after a parser fails to parse multiple lines. Patch by Bénédikt Tran.

  • gh-148254: Use singular “sec” instead of “secs” in timeit verbose output for consistency with other time units.

  • gh-148192: email.generator.Generator._make_boundary could fail to detect a duplicate boundary string if linesep was not n. It now correctly detects boundary strings when linesep is rn as well.

  • gh-146313: Fix a deadlock in multiprocessing’s resource tracker where the parent process could hang indefinitely in os.waitpid() during interpreter shutdown if a child created via os.fork() still held the resource tracker’s pipe open.

  • gh-145831: Fix email.quoprimime.decode() leaving a stray \r when eol='\r\n' by stripping the full eol string instead of one character.

  • gh-145105: Fix crash in csv reader when iterating with a re-entrant iterator that calls next() on the same reader from within __next__.

  • gh-105936: Attempting to mutate non-field attributes of dataclasses with both frozen and slots being True now raises FrozenInstanceError instead of TypeError. Their non-dataclass subclasses can now freely mutate non-field attributes, and the original non-slotted class can be garbage collected.

  • gh-140287: The asyncio REPL now handles exceptions when executing PYTHONSTARTUP scripts. Patch by Bartosz Sławecki.

  • gh-132631: Fix “I/O operation on closed file” when parsing JSON Lines file with JSON CLI.

  • gh-70039: Fixed bug where smtplib.SMTP.starttls() could fail if smtplib.SMTP.connect() is called explicitly rather than implicitly.

  • gh-83281: email: improve handling trailing garbage in address lists to avoid throwing AttributeError in certain edge cases

Documentation

Build

  • gh-149351: Avoid possible broken macOS framework install names when DESTDIR is specified during builds.

  • gh-146475: Block Apple Clang from being used to build the JIT as it ships without required LLVM tools.

  • gh-148535: No longer use the gcc -fprofile-update=atomic flag on i686. The flag has been added to fix a random GCC internal error on PGO build (gh-145801) caused by corruption of profile data (.gcda files). The problem is that it makes the PGO build way slower (up to 47x slower) on i686. Since the GCC internal error was not seen on i686 so far, don’t use -fprofile-update=atomic on i686 anymore. Patch by Victor Stinner.

  • gh-146264: Fix static module builds on non-WASI targets by linking HACL dependencies as static libraries when MODULE_BUILDTYPE=static, preventing duplicate _Py_LibHacl_* symbol errors at link time.

Windows

  • gh-149254: Updated bundled version of OpenSSL to 3.0.20.

  • gh-146458: Fix incorrect REPL height and width tracking on console window resize on Windows.

macOS

  • gh-149254: Update macOS installer to use OpenSSL 3.0.20.

Python 3.14.4 final

Release date: 2026-04-07

Security

Core and Builtins

  • gh-148157: Fix an unlikely crash when parsing an invalid type comments for function parameters. Found by OSS Fuzz in #492782951.

  • gh-148144: Initialize _PyInterpreterFrame.visited when copying interpreter frames so incremental GC does not read an uninitialized byte from generator and frame-object copies.

  • gh-146615: Fix a crash in __get__() for METH_METHOD descriptors when an invalid (non-type) object is passed as the second argument. Patch by Steven Sun.

  • gh-146308: Fixed several error handling issues in the _remote_debugging module, including safer validation of remote int objects, clearer asyncio task chain failures, and cache cleanup fixes that avoid leaking or double-freeing metadata on allocation failure. Patch by Pablo Galindo.

  • gh-146128: Fix a bug which could cause constant values to be partially corrupted in AArch64 JIT code. This issue is theoretical, and hasn’t actually been observed in unmodified Python interpreters.

  • gh-146250: Fixed a memory leak in SyntaxError when re-initializing it.

  • gh-146245: Fixed reference leaks in socket when audit hooks raise exceptions in socket.getaddrinfo() and socket.sendto().

  • gh-146196: Fix potential Undefined Behavior in PyUnicodeWriter_WriteASCII() by adding a zero-length check. Patch by Shamil Abdulaev.

  • gh-146227: Fix wrong type in _Py_atomic_load_uint16 in the C11 atomics backend (pyatomic_std.h), which used a 32-bit atomic load instead of 16-bit. Found by Mohammed Zuhaib.

  • gh-146056: Fix repr() for lists and tuples containing NULLs.

  • gh-146092: Handle properly memory allocation failures on str and float opcodes. Patch by Victor Stinner.

  • gh-146041: Fix free-threading scaling bottleneck in sys.intern() and PyObject_SetAttr() by avoiding the interpreter-wide lock when the string is already interned and immortalized.

  • gh-145990: python --help-env sections are now sorted by environment variable name.

  • gh-145990: python --help-xoptions is now sorted by -X option name.

  • gh-145376: Fix GC tracking in structseq.__replace__().

  • gh-145792: Fix out-of-bounds access when invoking faulthandler on a CPython build compiled without support for VLAs.

  • gh-142183: Avoid a pathological case where repeated calls at a specific stack depth could be significantly slower.

  • gh-145779: Improve scaling of classmethod() and staticmethod() calls in the free-threaded build by avoiding the descriptor __get__ call.

  • gh-145783: Fix an unlikely crash in the parser when certain errors were erroneously not propagated. Found by OSS Fuzz in #491369109.

  • gh-145685: Improve scaling of type attribute lookups in the free-threaded build by avoiding contention on the internal type lock.

  • gh-145701: Fix SystemError when __classdict__ or __conditional_annotations__ is in a class-scope inlined comprehension. Found by OSS Fuzz in #491105000.

  • gh-145713: Make bytearray.resize() thread-safe in the free-threaded build by using a critical section and calling the lock-held variant of the resize function.

  • gh-145615: Fixed a memory leak in the free-threaded build where mimalloc pages could become permanently unreclaimable until the owning thread exited.

  • gh-145566: In the free threading build, skip the stop-the-world pause when reassigning __class__ on a newly created object.

  • gh-145335: Fix a crash in os.pathconf() when called with -1 as the path argument.

  • gh-145036: In free-threaded build, fix race condition when calling __sizeof__() on a list

  • gh-145376: Fix reference leaks in various unusual error scenarios.

  • gh-145234: Fixed a SystemError in the parser when an encoding cookie (for example, UTF-7) decodes to carriage returns (\r). Newlines are now normalized after decoding in the string tokenizer.

    Patch by Pablo Galindo.

  • gh-130555: Fix use-after-free in dict.clear() when the dictionary values are embedded in an object and a destructor causes re-entrant mutation of the dictionary.

  • gh-145187: Fix compiler assertion fail when a type parameter bound contains an invalid expression in a conditional block.

  • gh-145142: Fix a crash in the free-threaded build when the dictionary argument to str.maketrans() is concurrently modified.

  • gh-144872: Fix heap buffer overflow in the parser found by OSS-Fuzz.

  • gh-144766: Fix a crash in fork child process when perf support is enabled.

  • gh-144759: Fix undefined behavior in the lexer when start and multi_line_start pointers are NULL in _PyLexer_remember_fstring_buffers() and _PyLexer_restore_fstring_buffers(). The NULL pointer arithmetic (NULL - valid_pointer) is now guarded with explicit NULL checks.

  • gh-144563: Fix interaction of the Tachyon profiler and ctypes and other modules that load the Python shared library (if present) in an independent map as this was causing the mechanism that loads the binary information to be confused. Patch by Pablo Galindo

  • gh-144601: Fix crash when importing a module whose PyInit function raises an exception from a subinterpreter.

  • gh-144438: Align the QSBR thread state array to a 64-byte cache line boundary to avoid false sharing in the free-threaded build.

  • gh-144513: Fix potential deadlock when using critical sections during stop-the-world pauses in the free-threaded build.

  • gh-144446: Fix data races in the free-threaded build when reading frame object attributes while another thread is executing the frame.

  • gh-143636: Fix a crash when calling SimpleNamespace.__replace__() on non-namespace instances. Patch by Bénédikt Tran.

  • gh-143650: Fix race condition in importlib where a thread could receive a stale module reference when another thread’s import fails.

  • gh-141732: Ensure the __repr__() for ExceptionGroup and BaseExceptionGroup does not change when the exception sequence that was original passed in to its constructor is subsequently mutated.

  • gh-140594: Fix an out of bounds read when a single NUL character is read from the standard input. Patch by Shamil Abdulaev.

  • gh-91636: While performing garbage collection, clear weakrefs to unreachable objects that are created during running of finalizers. If those weakrefs were are not cleared, they could reveal unreachable objects.

  • gh-130327: Fix erroneous clearing of an object’s __dict__ if overwritten at runtime.

  • gh-80667: Literals using the \N{name} escape syntax can now construct CJK ideographs and Hangul syllables using case-insensitive names.

Library

Documentation

  • gh-126676: Expand argparse documentation for type=bool with a demonstration of the surprising behavior and pointers to common alternatives.

  • gh-145649: Fix text wrapping and formatting of -X option descriptions in the python(1) man page by using proper roff markup.

  • gh-145450: Document missing public wave.Wave_write getter methods.

  • gh-136246: A new “Improve this page” link is available in the left-hand sidebar of the docs, offering links to create GitHub issues, discussion forum posts, or pull requests.

Tests

  • gh-144418: The Android testbed’s emulator RAM has been increased from 2 GB to 4 GB.

  • gh-146202: Fix a race condition in regrtest: make sure that the temporary directory is created in the worker process. Previously, temp_cwd() could fail on Windows if the “build” directory was not created. Patch by Victor Stinner.

  • gh-144739: When Python was compiled with system expat older then 2.7.2 but tests run with newer expat, still skip test.test_pyexpat.MemoryProtectionTest.

Build

  • gh-146541: The Android testbed can now be built for 32-bit ARM and x86 targets.

  • gh-146498: The iOS XCframework build script now ensures libpython isn’t included in installed app content, and is more robust in identifying standard library binary content that requires processing.

  • gh-146450: The Android build script was modified to improve parity with other platform build scripts.

  • gh-146446: The clean target for the Apple/iOS XCframework build script is now more selective when targeting a single architecture.

  • gh-145801: When Python build is optimized with GCC using PGO, use -fprofile-update=atomic option to use atomic operations when updating profile information. This option reduces the risk of gcov Data Files (.gcda) corruption which can cause random GCC crashes. Patch by Victor Stinner.

Windows

  • gh-145307: Defers loading of the psapi.dll module until it is used by ctypes.util.dllist().

  • gh-144551: Updated bundled version of OpenSSL to 3.0.19.

  • gh-140131: Fix REPL cursor position on Windows when module completion suggestion line hits console width.

macOS

C API

Python 3.14.3 final

Release date: 2026-02-03

Windows

  • gh-128067: Fix a bug in PyREPL on Windows where output without a trailing newline was overwritten by the next prompt.

Tools/Demos

  • gh-142095: Make gdb ‘py-bt’ command use frame from thread local state when available. Patch by Sam Gross and Victor Stinner.

Tests

  • gh-144415: The Android testbed now distinguishes between stdout/stderr messages which were triggered by a newline, and those triggered by a manual call to flush. This fixes logging of progress indicators and similar content.

  • gh-143460: Skip tests relying on infinite recusion if stack size is unlimited.

  • gh-65784: Add support for parametrized resource wantobjects in regrtests, which allows to run Tkinter tests with the specified value of tkinter.wantobjects, for example -u wantobjects=0.

  • gh-143553: Add support for parametrized resources, such as -u xpickle=2.7.

  • gh-142836: Accommodated Solaris in test_pdb.test_script_target_anonymous_pipe.

  • bpo-31391: Forward-port test_xpickle from Python 2 to Python 3 and add the resource back to test’s command line.

Security

  • gh-144125: BytesGenerator will now refuse to serialize (write) headers that are unsafely folded or delimited; see verify_generated_headers. (Contributed by Bas Bloemsaat and Petr Viktorin in gh-121650).

  • gh-143935: Fixed a bug in the folding of comments when flattening an email message using a modern email policy. Comments consisting of a very long sequence of non-foldable characters could trigger a forced line wrap that omitted the required leading space on the continuation line, causing the remainder of the comment to be interpreted as a new header field. This enabled header injection with carefully crafted inputs.

  • gh-143925: Reject control characters in data: URL media types.

  • gh-143919: Reject control characters in http.cookies.Morsel fields and values.

  • gh-143916: Reject C0 control characters within wsgiref.headers.Headers fields, values, and parameters.

Library

  • gh-144380: Improve performance of io.BufferedReader line iteration by ~49%.

  • gh-144169: Fix three crashes when non-string keyword arguments are supplied to objects in the ast module.

  • gh-144100: Fixed a crash in ctypes when using a deprecated POINTER(str) type in argtypes. Instead of aborting, ctypes now raises a proper Python exception when the pointer target type is unresolved.

  • gh-144050: Fix stat.filemode() in the pure-Python implementation to avoid misclassifying invalid mode values as block devices.

  • gh-144023: Fixed validation of file descriptor 0 in posix functions when used with follow_symlinks parameter.

  • gh-143999: Fix an issue where inspect.getgeneratorstate() and inspect.getcoroutinestate() could fail for generators wrapped by types.coroutine() in the suspended state.

  • gh-143831: annotationlib.ForwardRef objects are now hashable when created from annotation scopes with closures. Previously, hashing such objects would throw an exception. Patch by Bartosz Sławecki.

  • gh-143874: Fixed a bug in pdb where expression results were not sent back to remote client.

  • gh-143880: Fix data race in functools.partial() in the free threading build.

  • gh-143706: Fix multiprocessing forkserver so that sys.argv is correctly set before __main__ is preloaded. Previously, sys.argv was empty during main module import in forkserver child processes. This fixes a regression introduced in 3.13.8 and 3.14.1. Root caused by Aaron Wieczorek, test provided by Thomas Watson, thanks!

  • gh-143638: Forbid reentrant calls of the pickle.Pickler and pickle.Unpickler methods for the C implementation. Previously, this could cause crash or data corruption, now concurrent calls of methods of the same object raise RuntimeError.

  • gh-78724: Raise RuntimeError’s when user attempts to call methods on half-initialized Struct objects, For example, created by Struct.__new__(Struct). Patch by Sergey B Kirpichev.

  • gh-143196: Fix crash when the internal encoder object returned by undocumented function json.encoder.c_make_encoder() was called with non-zero second (_current_indent_level) argument.

  • gh-143191: _thread.stack_size() now raises ValueError if the stack size is too small. Patch by Victor Stinner.

  • gh-143602: Fix a inconsistency issue in write() that leads to unexpected buffer overwrite by deduplicating the buffer exports.

  • gh-143547: Fix sys.unraisablehook() when the hook raises an exception and changes sys.unraisablehook(): hold a strong reference to the old hook. Patch by Victor Stinner.

  • gh-143517: annotationlib.get_annotations() no longer raises a SyntaxError when evaluating a stringified starred annotation that starts with one or more whitespace characters followed by a *. Patch by Bartosz Sławecki.

  • gh-143378: Fix use-after-free crashes when a BytesIO object is concurrently mutated during write() or writelines().

  • gh-143346: Fix incorrect wrapping of the Base64 data in plistlib._PlistWriter when the indent contains a mix of tabs and spaces.

  • gh-143310: tkinter: fix a crash when a Python list is mutated during the conversion to a Tcl object (e.g., when setting a Tcl variable). Patch by Bénédikt Tran.

  • gh-143309: Fix a crash in os.execve() on non-Windows platforms when given a custom environment mapping which is then mutated during parsing. Patch by Bénédikt Tran.

  • gh-143308: pickle: fix use-after-free crashes when a PickleBuffer is concurrently mutated by a custom buffer callback during pickling. Patch by Bénédikt Tran and Aaron Wieczorek.

  • gh-143237: Fix support of named pipes in the rotating logging handlers.

  • gh-143249: Fix possible buffer leaks in Windows overlapped I/O on error handling.

  • gh-143241: zoneinfo: fix infinite loop in ZoneInfo.from_file when parsing a malformed TZif file. Patch by Fatih Celik.

  • gh-142830: sqlite3: fix use-after-free crashes when the connection’s callbacks are mutated during a callback execution. Patch by Bénédikt Tran.

  • gh-143200: xml.etree.ElementTree: fix use-after-free crashes in __getitem__() and __setitem__() methods of Element when the element is concurrently mutated. Patch by Bénédikt Tran.

  • gh-142195: Updated timeout evaluation logic in subprocess to be compatible with deterministic environments like Shadow where time moves exactly as requested.

  • gh-142164: Fix the ctypes bitfield overflow error message to report the correct offset and size calculation.

  • gh-143145: Fixed a possible reference leak in ctypes when constructing results with multiple output parameters on error.

  • gh-122431: Corrected the error message in readline.append_history_file() to state that nelements must be non-negative instead of positive.

  • gh-143004: Fix a potential use-after-free in collections.Counter.update() when user code mutates the Counter during an update.

  • gh-143046: The asyncio REPL no longer prints copyright and version messages in the quiet mode (-q). Patch by Bartosz Sławecki.

  • gh-140648: The asyncio REPL now respects the -I flag (isolated mode). Previously, it would load and execute PYTHONSTARTUP even if the flag was set. Contributed by Bartosz Sławecki.

  • gh-142991: Fixed socket operations such as recvfrom() and sendto() for FreeBSD divert(4) socket.

  • gh-143010: Fixed a bug in mailbox where the precise timing of an external event could result in the library opening an existing file instead of a file it expected to create.

  • gh-142881: Fix concurrent and reentrant call of atexit.unregister().

  • gh-112127: Fix possible use-after-free in atexit.unregister() when the callback is unregistered during comparison.

  • gh-142783: Fix zoneinfo use-after-free with descriptor _weak_cache. a descriptor as _weak_cache could cause crashes during object creation. The fix ensures proper reference counting for descriptor-provided objects.

  • gh-142754: Add the ownerDocument attribute to xml.dom.minidom elements and attributes created by directly instantiating the Element or Attr class. Note that this way of creating nodes is not supported; creator functions like xml.dom.Document.documentElement() should be used instead.

  • gh-142784: The asyncio REPL now properly closes the loop upon the end of interactive session. Previously, it could cause surprising warnings. Contributed by Bartosz Sławecki.

  • gh-142555: array: fix a crash in a[i] = v when converting i to an index via i.__index__ or i.__float__ mutates the array.

  • gh-142594: Fix crash in TextIOWrapper.close() when the underlying buffer’s closed property calls detach().

  • gh-142451: hmac: Ensure that the HMAC.block_size attribute is correctly copied by HMAC.copy. Patch by Bénédikt Tran.

  • gh-142495: collections.defaultdict now prioritizes __setitem__() when inserting default values from default_factory. This prevents race conditions where a default value would overwrite a value set before default_factory returns.

  • gh-142651: unittest.mock: fix a thread safety issue where Mock.call_count may return inaccurate values when the mock is called concurrently from multiple threads.

  • gh-142595: Added type check during initialization of the decimal module to prevent a crash in case of broken stdlib. Patch by Sergey B Kirpichev.

  • gh-142556: Fix crash when a task gets re-registered during finalization in asyncio. Patch by Kumar Aditya.

  • gh-123241: Avoid reference count operations in garbage collection of ctypes objects.

  • gh-142517: The non-compat32 email policies now correctly handle refolding encoded words that contain bytes that can not be decoded in their specified character set. Previously this resulted in an encoding exception during folding.

  • gh-112527: The help text for required options in argparse no longer extended with “ (default: None)”.

  • gh-142346: Fix usage formatting for mutually exclusive groups in argparse when they are preceded by positional arguments or followed or intermixed with other optional arguments.

  • gh-142315: Pdb can now run scripts from anonymous pipes used in process substitution. Patch by Bartosz Sławecki.

  • gh-142332: Fix usage formatting for positional arguments in mutually exclusive groups in argparse. in argparse.

  • gh-142282: Fix winreg.QueryValueEx() to not accidentally read garbage buffer under race condition.

  • gh-75949: Fix argparse to preserve | separators in mutually exclusive groups when the usage line wraps due to length.

  • gh-142267: Improve argparse performance by caching the formatter used for argument validation.

  • gh-68552: MisplacedEnvelopeHeaderDefect and Missing header name defects are now correctly passed to the handle_defect method of policy in FeedParser.

  • gh-142006: Fix a bug in the email.policy.default folding algorithm which incorrectly resulted in a doubled newline when a line ending at exactly max_line_length was followed by an unfoldable token.

  • gh-105836: Fix asyncio.run_coroutine_threadsafe() leaving underlying cancelled asyncio task running.

  • gh-139971: pydoc: Ensure that the link to the online documentation of a stdlib module is correct.

  • gh-139262: Some keystrokes can be swallowed in the new PyREPL on Windows, especially when used together with the ALT key. Fix by Chris Eibl.

  • gh-138897: Improved license/copyright/credits display in the REPL: now uses a pager.

  • gh-79986: Add parsing for References and In-Reply-To headers to the email library that parses the header content as lists of message id tokens. This prevents them from being folded incorrectly.

  • gh-136282: Add support for UNNAMED_SECTION when creating a section via the mapping protocol access

  • gh-109263: Starting a process from spawn context in multiprocessing no longer sets the start method globally.

  • gh-133253: Fix thread-safety issues in linecache.

  • gh-132715: Skip writing objects during marshalling once a failure has occurred.

IDLE

  • gh-143774: Better explain the operation of Format / Format Paragraph.

Documentation

Core and Builtins

  • gh-144307: Prevent a reference leak in module teardown at interpreter finalization.

  • gh-144194: Fix error handling in perf jitdump initialization on memory allocation failure.

  • gh-144012: Check if the result is NULL in BINARY_OP_EXTENT opcode.

  • gh-141805: Fix crash in set when objects with the same hash are concurrently added to the set after removing an element with the same hash while the set still contains elements with the same hash.

  • gh-143670: Fixes a crash in ga_repr_items_list function.

  • gh-143377: Fix a crash in _interpreters.capture_exception() when the exception is incorrectly formatted. Patch by Bénédikt Tran.

  • gh-136924: The interactive help mode in the REPL no longer incorrectly syntax highlights text input as Python code. Contributed by Olga Matoula.

  • gh-143189: Fix crash when inserting a non-str key into a split table dictionary when the key matches an existing key in the split table but has no corresponding value in the dict.

  • gh-143228: Fix use-after-free in perf trampoline when toggling profiling while threads are running or during interpreter finalization with daemon threads active. The fix uses reference counting to ensure trampolines are not freed while any code object could still reference them. Pach by Pablo Galindo

  • gh-142664: Fix a use-after-free crash in memoryview.__hash__ when the __hash__ method of the referenced object mutates that object or the view. Patch by Bénédikt Tran.

  • gh-142557: Fix a use-after-free crash in bytearray.__mod__ when the bytearray is mutated while formatting the %-style arguments. Patch by Bénédikt Tran.

  • gh-143195: Fix use-after-free crashes in bytearray.hex() and memoryview.hex() when the separator’s __len__() mutates the original object. Patch by Bénédikt Tran.

  • gh-142975: Fix crash after unfreezing all objects tracked by the garbage collector on the free threaded build.

  • gh-143135: Set sys.flags.inspect to 1 when PYTHONINSPECT is 0. Previously, it was set to 0 in this case.

  • gh-143003: Fix an overflow of the shared empty buffer in bytearray.extend() when __length_hint__() returns 0 for non-empty iterator.

  • gh-143006: Fix a possible assertion error when comparing negative non-integer float and int with the same number of bits in the integer part.

  • gh-143057: Avoid locking in PyTraceMalloc_Track() and PyTraceMalloc_Untrack() when tracemalloc is not enabled.

  • gh-142776: Fix a file descriptor leak in import.c

  • gh-142829: Fix a use-after-free crash in contextvars.Context comparison when a custom __eq__ method modifies the context via set().

  • gh-142766: Clear the frame of a generator when generator.close() is called.

  • gh-142737: Tracebacks will be displayed in fallback mode even if io.open() is lost. Previously, this would crash the interpreter. Patch by Bartosz Sławecki.

  • gh-142554: Fix a crash in divmod() when _pylong.int_divmod() does not return a tuple of length two exactly. Patch by Bénédikt Tran.

  • gh-142560: Fix use-after-free in bytearray search-like methods (find(), count(), index(), rindex(), and rfind()) by marking the storage as exported which causes reallocation attempts to raise BufferError. For contains(), split(), and rsplit() the buffer protocol is used for this.

  • gh-142531: Fix a free-threaded GC performance regression. If there are many untracked tuples, the GC will run too often, resulting in poor performance. The fix is to include untracked tuples in the “long lived” object count. The number of frozen objects is also now included since the free-threaded GC must scan those too.

  • gh-142402: Fix reference counting when adjacent literal parts are merged while constructing string.templatelib.Template, preventing the displaced string object from leaking.

  • gh-133932: Fix crash in the free threading build when clearing frames that hold tagged integers.

  • gh-142343: Fix SIGILL crash on m68k due to incorrect assembly constraint.

  • gh-100964: Fix reference cycle in exhausted generator frames. Patch by Savannah Ostrowski.

  • gh-69605: Fix edge-cases around already imported modules in the REPL auto-completion of imports.

  • gh-138568: Adjusted the built-in help() function so that empty inputs are ignored in interactive mode.

  • gh-137007: Fix a bug during JIT compilation failure which caused garbage collection debug assertions to fail.

C API

Build

  • gh-142454: When calculating the digest of the JIT stencils input, sort the hashed files by filenames before adding their content to the hasher. This ensures deterministic hash input and hence deterministic hash, independent on filesystem order.

  • gh-141808: When running make clean-retain-profile, keep the generated JIT stencils. That way, the stencils are not generated twice when Profile-guided optimization (PGO) is used. It also allows distributors to supply their own pre-built JIT stencils.

  • gh-138061: Ensure reproducible builds by making JIT stencil header generation deterministic.

Python 3.14.2 final

Release date: 2025-12-05

Security

  • gh-142145: Remove quadratic behavior in xml.minidom node ID cache clearing.

  • gh-119452: Fix a potential memory denial of service in the http.server module. When a malicious user is connected to the CGI server on Windows, it could cause an arbitrary amount of memory to be allocated. This could have led to symptoms including a MemoryError, swapping, out of memory (OOM) killed processes or containers, or even system crashes.

Library

  • gh-140797: Revert changes to the undocumented re.Scanner class. Capturing groups are still allowed for backward compatibility, although using them can lead to incorrect result. They will be forbidden in future Python versions.

  • gh-142206: The resource tracker in the multiprocessing module now uses the original communication protocol, as in Python 3.14.0 and below, by default. This avoids issues with upgrading Python while it is running. (Note that such ‘in-place’ upgrades are not tested.) The tracker remains compatible with subprocesses that use new protocol (that is, subprocesses using Python 3.13.10, 3.14.1 and 3.15).

  • gh-142214: Fix two regressions in dataclasses in Python 3.14.1 related to annotations.

    • An exception is no longer raised if slots=True is used and the __init__ method does not have an __annotate__ attribute (likely because init=False was used).

    • An exception is no longer raised if annotations are requested on the __init__ method and one of the fields is not present in the class annotations. This can occur in certain dynamic scenarios.

    Patch by Jelle Zijlstra.

Core and Builtins

  • gh-142218: Fix crash when inserting into a split table dictionary with a non str key that matches an existing key.

Library

  • gh-116738: Fix cmath data race when initializing trigonometric tables with subinterpreters.

Python 3.14.1 final

Release date: 2025-12-02

Windows

  • gh-139810: Installing with py install 3[.x]-dev will now select final versions as well as prereleases.

Tools/Demos

  • gh-141692: Each slice of an iOS XCframework now contains a lib folder that contains a symlink to the libpython dylib. This allows binary modules to be compiled for iOS using dynamic libreary linking, rather than Framework linking.

  • gh-141442: The iOS testbed now correctly handles test arguments that contain spaces.

  • gh-140702: The iOS testbed app will now expose the GITHUB_ACTIONS environment variable to iOS apps being tested.

  • gh-137484: Have Tools/wasm/wasi put the build Python into a directory named after the build triple instead of “build”.

  • gh-137248: Add a --logdir option to Tools/wasm/wasi for specifying where to write log files.

  • gh-137243: Have Tools/wasm/wasi detect a WASI SDK install in /opt when it was directly extracted from a release tarball.

Tests

  • gh-140482: Preserve and restore the state of stty echo as part of the test environment.

  • gh-140082: Update python -m test to set FORCE_COLOR=1 when being run with color enabled so that unittest which is run by it with redirected output will output in color.

  • gh-139208: Fix regrtest --fast-ci --verbose: don’t ignore the --verbose option anymore. Patch by Victor Stinner.

  • gh-136442: Use exitcode 1 instead of 5 if unittest.TestCase.setUpClass() raises an exception

Security

  • gh-139700: Check consistency of the zip64 end of central directory record. Support records with “zip64 extensible data” if there are no bytes prepended to the ZIP file.

  • gh-139283: sqlite3: correctly handle maximum number of rows to fetch in Cursor.fetchmany and reject negative values for Cursor.arraysize. Patch by Bénédikt Tran.

  • gh-137836: Add support of the “plaintext” element, RAWTEXT elements “xmp”, “iframe”, “noembed” and “noframes”, and optionally RAWTEXT element “noscript” in html.parser.HTMLParser.

  • gh-136063: email.message: ensure linear complexity for legacy HTTP parameters parsing. Patch by Bénédikt Tran.

  • gh-136065: Fix quadratic complexity in os.path.expandvars().

  • gh-119451: Fix a potential memory denial of service in the http.client module. When connecting to a malicious server, it could cause an arbitrary amount of memory to be allocated. This could have led to symptoms including a MemoryError, swapping, out of memory (OOM) killed processes or containers, or even system crashes.

  • gh-119342: Fix a potential memory denial of service in the plistlib module. When reading a Plist file received from untrusted source, it could cause an arbitrary amount of memory to be allocated. This could have led to symptoms including a MemoryError, swapping, out of memory (OOM) killed processes or containers, or even system crashes.

Library

IDLE

  • gh-96491: Deduplicate version number in IDLE shell title bar after saving to a file.

  • gh-139742: Colorize t-string prefixes for template strings in IDLE, as done for f-string prefixes.

Documentation

Core and Builtins

  • gh-142048: Fix quadratically increasing garbage collection delays in free-threaded build.

Library

  • gh-116738: Fix thread safety issue with re scanner objects in free-threaded builds.

Core and Builtins

  • gh-141930: When importing a module, use Python’s regular file object to ensure that writes to .pyc files are complete or an appropriate error is raised.

  • gh-120158: Fix inconsistent state when enabling or disabling monitoring events too many times.

  • gh-139653: Only raise a RecursionError or trigger a fatal error if the stack pointer is both below the limit pointer and above the stack base. If outside of these bounds assume that it is OK. This prevents false positives when user-space threads swap stacks.

  • gh-139103: Improve multithreaded scaling of dataclasses on the free-threaded build.

  • gh-141579: Fix sys.activate_stack_trampoline() to properly support the perf_jit backend. Patch by Pablo Galindo.

  • gh-114203: Skip locking if object is already locked by two-mutex critical section.

  • gh-141528: Suggest using concurrent.interpreters.Interpreter.close() instead of the private _interpreters.destroy function when warning about remaining subinterpreters. Patch by Sergey Miryanov.

  • gh-141312: Fix the assertion failure in the __setstate__ method of the range iterator when a non-integer argument is passed. Patch by Sergey Miryanov.

Library

Core and Builtins

Library

  • gh-140260: Fix struct data race in endian table initialization with subinterpreters. Patch by Shamil Abdulaev.

Core and Builtins

Library

Core and Builtins

  • gh-140406: Fix memory leak when an object’s __hash__() method returns an object that isn’t an int.

  • gh-140358: Restore elapsed time and unreachable object count in GC debug output. These were inadvertently removed during a refactor of gc.c. The debug log now again reports elapsed collection time and the number of unreachable objects. Contributed by Pål Grønås Drange.

  • gh-140306: Fix memory leaks in cross-interpreter channel operations and shared namespace handling.

  • gh-140301: Fix memory leak of PyConfig in subinterpreters.

  • gh-140257: Fix data race between interpreter_clear() and take_gil() on eval_breaker during finalization with daemon threads.

  • gh-139951: Fixes a regression in GC performance for a growing heap composed mostly of small tuples.

    • Counts number of actually tracked objects, instead of trackable objects. This ensures that untracking tuples has the desired effect of reducing GC overhead.

    • Does not track most untrackable tuples during creation. This prevents large numbers of small tuples causing excessive GCs.

  • gh-140104: Fix a bug with exception handling in the JIT. Patch by Ken Jin. Bug reported by Daniel Diniz.

  • gh-140061: Fixing the checking of whether an object is uniquely referenced to ensure free-threaded compatibility. Patch by Sergey Miryanov.

  • gh-140067: Fix memory leak in sub-interpreter creation.

  • gh-140000: Fix potential memory leak when a reference cycle exists between an instance of typing.TypeAliasType, typing.TypeVar, typing.ParamSpec, or typing.TypeVarTuple and its __name__ attribute. Patch by Mikhail Efimov.

  • gh-139914: Restore support for HP PA-RISC, which has an upwards-growing stack.

  • gh-139988: Fix a memory leak when failing to create a Union type. Patch by Bénédikt Tran.

  • gh-139748: Fix reference leaks in error branches of functions accepting path strings or bytes such as compile() and os.system(). Patch by Bénédikt Tran.

  • gh-139516: Fix lambda colon erroneously start format spec in f-string in tokenizer.

  • gh-139640: ast.parse() no longer emits syntax warnings for return/break/continue in finally (see PEP 765) – they are only emitted during compilation.

  • gh-139640: Fix swallowing some syntax warnings in different modules if they accidentally have the same message and are emitted from the same line. Fix duplicated warnings in the finally block.

  • gh-63161: Support non-UTF-8 shebang and comments in Python source files if non-UTF-8 encoding is specified. Detect decoding error in comments for default (UTF-8) encoding. Show the line and position of decoding error for default encoding in a traceback. Show the line containing the coding cookie when it conflicts with the BOM in a traceback.

Library

Core and Builtins

  • gh-138558: Fix handling of unusual t-string annotations in annotationlib. Patch by Dave Peck.

  • gh-134466: Don’t run PyREPL in a degraded environment where setting termios attributes is not allowed.

  • gh-138944: Fix SyntaxError message when invalid syntax appears on the same line as a valid import ... as ... or from ... import ... as ... statement. Patch by Brian Schubert.

  • gh-105487: Remove non-existent __copy__(), __deepcopy__(), and __bases__ from the __dir__() entries of types.GenericAlias.

  • gh-69605: Fix some standard library submodules missing from the REPL auto-completion of imports.

Library

  • gh-116738: Make cProfile thread-safe on the free threaded build.

  • gh-138004: On Solaris/Illumos platforms, thread names are now encoded as ASCII to avoid errors on systems (e.g. OpenIndiana) that don’t support non-ASCII names.

Core and Builtins

C API

Build

  • gh-141808: Do not generate the jit stencils twice in case of PGO builds on Windows.

  • gh-141784: Fix _remote_debugging_module.c compilation on 32-bit Linux. Include Python.h before system headers to make sure that _remote_debugging_module.c uses the same types (ABI) than Python. Patch by Victor Stinner.

  • gh-140768: Warn when the WASI SDK version doesn’t match what’s supported.

  • gh-140513: Generate a clear compilation error when _Py_TAIL_CALL_INTERP is enabled but either preserve_none or musttail is not supported.

  • gh-140189: iOS builds were added to CI.

  • gh-138489: When cross-compiling for WASI by build_wasm or build_emscripten, the build-details.json step is now included in the build process, just like with native builds.

    This fixes the libinstall task which requires the build-details.json file during the process.

  • gh-137618: PYTHON_FOR_REGEN now requires Python 3.10 to Python 3.15. Patch by Adam Turner.

  • gh-123681: Check the strftime() behavior at runtime instead of at the compile time to support cross-compiling. Remove the internal macro _Py_NORMALIZE_CENTURY.

Python 3.14.0 final

Release date: 2025-10-07

macOS

  • gh-124111: Update macOS installer to use Tcl/Tk 8.6.17.

  • gh-139573: Updated bundled version of OpenSSL to 3.0.18.

Windows

  • gh-139573: Updated bundled version of OpenSSL to 3.0.18.

Tools/Demos

  • gh-139330: SBOM generation tool didn’t cross-check the version and checksum values against the Modules/expat/refresh.sh script, leading to the values becoming out-of-date during routine updates.

  • gh-132006: XCframeworks now include privacy manifests to satisfy Apple App Store submission requirements.

  • gh-138171: A script for building an iOS XCframework was added. As part of this change, the top level iOS folder has been moved to be a subdirectory of the Apple folder.

Security

Library

  • gh-139312: Upgrade bundled libexpat to 2.7.3

Python 3.14.0 release candidate 3

Release date: 2025-09-18

Windows

  • gh-138896: Fix error installing C runtime on non-updated Windows machines

Tools/Demos

  • gh-137873: The iOS test runner has been simplified, resolving some issues that have been observed using the runner in GitHub Actions and Azure Pipelines test environments.

Security

  • gh-135661: Fix CDATA section parsing in html.parser.HTMLParser according to the HTML5 standard: ] ]> and ]] > no longer end the CDATA section. Add private method _set_support_cdata() which can be used to specify how to parse <[CDATA[ — as a CDATA section in foreign content (SVG or MathML) or as a bogus comment in the HTML namespace.

Library

Core and Builtins

  • gh-71810: Raise OverflowError for (-1).to_bytes() for signed conversions when bytes count is zero. Patch by Sergey B Kirpichev.

  • gh-138192: Fix contextvars initialization so that all subinterpreters are assigned the MISSING value.

  • gh-138479: Fix a crash when a generic object’s __typing_subst__ returns an object that isn’t a tuple.

  • gh-138372: Fix SyntaxWarning emitted for erroneous subscript expressions involving template string literals. Patch by Brian Schubert.

  • gh-138318: The default REPL now avoids highlighting built-in names (for instance set or format()) when they are used as attribute names (for instance in value.set or text.format).

  • gh-138349: Fix crash in certain cases where a module contains both a module-level annotation and a comprehension.

  • gh-137384: Fix a crash when using the warnings module in a finalizer at shutdown. Patch by Kumar Aditya.

  • gh-137883: Fix runaway recursion when calling a function with keyword arguments.

  • gh-137079: Fix keyword typo recognition when parsing files. Patch by Pablo Galindo.

  • gh-137728: Fix the JIT’s handling of many local variables. This previously caused a segfault.

  • gh-137576: Fix for incorrect source code being shown in tracebacks from the Basic REPL when PYTHONSTARTUP is given. Patch by Adam Hartz.

Python 3.14.0 release candidate 2

Release date: 2025-08-14

macOS

  • gh-137450: macOS installer shell path management improvements: separate the installer Shell profile updater postinstall script from the Update Shell Profile.command to enable more robust error handling.

  • gh-137134: Update macOS installer to ship with SQLite version 3.50.4.

Windows

  • gh-137134: Update Windows installer to ship with SQLite 3.50.4.

Library

  • gh-137426: Remove the code deprecation of importlib.abc.ResourceLoader. It is documented as deprecated, but left for backwards compatibility with other classes in importlib.abc.

  • gh-137282: Fix tab completion and dir() on concurrent.futures.

  • gh-137257: Bump the version of pip bundled in ensurepip to version 25.2

  • gh-137226: Fix behavior of annotationlib.ForwardRef.evaluate() when the type_params parameter is passed and the name of a type param is also present in an enclosing scope.

  • gh-130522: Fix unraisable TypeError raised during interpreter shutdown in the threading module.

  • gh-137059: Fix handling of file URLs with a Windows drive letter in the URL authority by urllib.request.url2pathname(). This fixes a regression in earlier pre-releases of Python 3.14.

  • gh-130577: tarfile now validates archives to ensure member offsets are non-negative. (Contributed by Alexander Enrique Urieles Nieto in gh-130577.)

  • gh-135228: When dataclasses replaces a class with a slotted dataclass, the original class can now be garbage collected again. Earlier changes in Python 3.14 caused this class to always remain in existence together with the replacement class synthesized by dataclasses.

Documentation

  • gh-136155: We are now checking for fatal errors in EPUB builds in CI.

Core and Builtins

  • gh-137400: Fix a crash in the free threading build when disabling profiling or tracing across all threads with PyEval_SetProfileAllThreads() or PyEval_SetTraceAllThreads() or their Python equivalents threading.settrace_all_threads() and threading.setprofile_all_threads().

  • gh-137314: Fixed a regression where raw f-strings incorrectly interpreted escape sequences in format specifications. Raw f-strings now properly preserve literal backslashes in format specs, matching the behavior from Python 3.11. For example, rf"{obj:\xFF}" now correctly produces '\\xFF' instead of 'ÿ'. Patch by Pablo Galindo.

  • gh-137308: A standalone docstring in a node body is optimized as a pass statement to ensure that the node’s body is never empty. There was a ValueError in compile() otherwise.

  • gh-137288: Fix bug where some bytecode instructions of a boolean expression are not associated with the correct exception handler.

  • gh-134291: Remove some newer macOS API usage from the JIT compiler in order to restore compatibility with older OSX 10.15 deployment targets.

  • gh-131338: Disable computed stack limit checks on non-glibc linux platforms to fix crashes on deep recursion.

  • gh-136870: Fix data races while de-instrumenting bytecode of code objects running concurrently in threads.

C API

Build

Python 3.14.0 release candidate 1

Release date: 2025-07-22

Tools/Demos

  • gh-136251: Fixes and usability improvements for Tools/wasm/emscripten/web_example

Security

Library

Core and Builtins

  • gh-136801: Fix PyREPL syntax highlighting on match cases after multi-line case. Contributed by Olga Matoula.

Library

Core and Builtins

  • gh-136541: Fix some issues with the perf trampolines on x86-64 and aarch64. The trampolines were not being generated correctly for some cases, which could lead to the perf integration not working correctly. Patch by Pablo Galindo.

  • gh-136517: Fixed a typo that prevented printing of uncollectable objects when the gc.DEBUG_UNCOLLECTABLE mode was set.

  • gh-136525: Fix issue where per-thread bytecode was not instrumented for newly created threads.

  • gh-132661: Interpolation.expression now has a default, the empty string.

  • gh-132661: Reflect recent PEP 750 change.

    Disallow concatenation of string.templatelib.Template and str. Also, disallow implicit concatenation of t-string literals with string or f-string literals.

Library

Core and Builtins

  • gh-135148: Fixed a bug where f-string debug expressions (using =) would incorrectly strip out parts of strings containing escaped quotes and # characters. Patch by Pablo Galindo.

  • gh-133136: Limit excess memory usage in the free threading build when a large dictionary or list is resized and accessed by multiple threads.

  • gh-91153: Fix a crash when a bytearray is concurrently mutated during item assignment.

  • gh-127971: Fix off-by-one read beyond the end of a string in string search.

C API

Build

  • gh-135621: PyREPL no longer depends on the curses standard library. Contributed by Łukasz Langa.

Python 3.14.0 beta 4

Release date: 2025-07-08

Tools/Demos

  • gh-135968: Stubs for strip are now provided as part of an iOS install.

  • gh-133600: Backport file reorganization for Tools/wasm/wasi.

    This should make backporting future code changes easier. It also simplifies instructions around how to do WASI builds in the devguide.

Tests

  • gh-135966: The iOS testbed now handles the app_packages folder as a site directory.

  • gh-135494: Fix regrtest to support excluding tests from --pgo tests. Patch by Victor Stinner.

Security

  • gh-136053: marshal: fix a possible crash when deserializing slice objects.

  • gh-135661: Fix parsing start and end tags in html.parser.HTMLParser according to the HTML5 standard.

    • Whitespaces no longer accepted between </ and the tag name. E.g. </ script> does not end the script section.

    • Vertical tabulation (\v) and non-ASCII whitespaces no longer recognized as whitespaces. The only whitespaces are \t\n\r\f and space.

    • Null character (U+0000) no longer ends the tag name.

    • Attributes and slashes after the tag name in end tags are now ignored, instead of terminating after the first > in quoted attribute value. E.g. </script/foo=">"/>.

    • Multiple slashes and whitespaces between the last attribute and closing > are now ignored in both start and end tags. E.g. <a foo=bar/ //>.

    • Multiple = between attribute name and value are no longer collapsed. E.g. <a foo==bar> produces attribute “foo” with value “=bar”.

    • [Reverted in gh-136927] Whitespaces between the = separator and attribute name or value are no longer ignored. E.g. <a foo =bar> produces two attributes “foo” and “=bar”, both with value None; <a foo= bar> produces two attributes: “foo” with value “” and “bar” with value None.

  • gh-102555: Fix comment parsing in html.parser.HTMLParser according to the HTML5 standard. --!> now ends the comment. -- > no longer ends the comment. Support abnormally ended empty comments <--> and <--->.

Library

Documentation

  • gh-136155: EPUB builds are fixed by excluding non-XHTML-compatible tags.

Core and Builtins

  • gh-109700: Fix memory error handling in PyDict_SetDefault().

  • gh-78465: Fix error message for cls.__new__(cls, ...) where cls is not instantiable builtin or extension type (with tp_new set to NULL).

  • gh-129958: Differentiate between t-strings and f-strings in syntax error for newlines in format specifiers of single-quoted interpolated strings.

  • gh-135871: Non-blocking mutex lock attempts now return immediately when the lock is busy instead of briefly spinning in the free threading build.

  • gh-135106: Restrict the trashcan mechanism to GC’ed objects and untrack them while in the trashcan to prevent the GC and trashcan mechanisms conflicting.

  • gh-135607: Fix potential weakref races in an object’s destructor on the free threaded build.

  • gh-135608: Fix a crash in the JIT involving attributes of modules.

  • gh-135543: Emit sys.remote_exec audit event when sys.remote_exec() is called and migrate remote_debugger_script to cpython.remote_debugger_script.

  • gh-134280: Disable constant folding for ~ with a boolean argument. This moves the deprecation warning from compile time to runtime.

C API

  • gh-135906: Fix compilation errors when compiling the internal headers with a C++ compiler.

Build

  • gh-134273: Add support for configuring compiler flags for the JIT with CFLAGS_JIT

Python 3.14.0 beta 3

Release date: 2025-06-17

Windows

  • gh-135099: Fix a crash that could occur on Windows when a background thread waits on a PyMutex while the main thread is shutting down the interpreter.

Tests

  • gh-132815: Fix test__opcode: add JUMP_BACKWARD to specialization stats.

  • gh-135489: Show verbose output for failing tests during PGO profiling step with –enable-optimizations.

  • gh-135120: Add test.support.subTests().

Security

  • gh-135462: Fix quadratic complexity in processing specially crafted input in html.parser.HTMLParser. End-of-file errors are now handled according to the HTML5 specs – comments and declarations are automatically closed, tags are ignored.

  • gh-135034: Fixes multiple issues that allowed tarfile extraction filters (filter="data" and filter="tar") to be bypassed using crafted symlinks and hard links.

    Addresses CVE 2024-12718, CVE 2025-4138, CVE 2025-4330, and CVE 2025-4517.

Library

  • gh-65697: configparser’s error message when attempting to write an invalid key is now more helpful.

  • gh-135497: Fix os.getlogin() failing for longer usernames on BSD-based platforms.

  • gh-135429: Fix the argument mismatch in _lsprof for PY_THROW event.

  • gh-135368: Fix unittest.mock.Mock generation on dataclasses.dataclass() objects. Now all special attributes are set as it was before gh-124429.

  • gh-133967: Do not normalize locale name ‘C.UTF-8’ to ‘en_US.UTF-8’.

  • gh-135321: Raise a correct exception for values greater than 0x7fffffff for the BINSTRING opcode in the C implementation of pickle.

  • gh-135276: Backported bugfixes in zipfile.Path from zipp 3.23. Fixed .name, .stem and other basename-based properties on Windows when working with a zipfile on disk.

  • gh-135244: uuid: when the MAC address cannot be determined, the 48-bit node ID is now generated with a cryptographically-secure pseudo-random number generator (CSPRNG) as per RFC 9562, §6.10.3. This affects uuid1() and uuid6().

  • gh-134970: Fix the “unknown action” exception in argparse.ArgumentParser.add_argument_group() to correctly replace the action class.

  • gh-134718: ast.dump() now only omits None and [] values if they are default values.

  • gh-134939: Add the concurrent.interpreters module. See PEP 734.

  • gh-134885: Fix possible crash in the compression.zstd module related to setting parameter types. Patch by Jelle Zijlstra.

  • gh-134857: Improve error report for doctests run with unittest. Remove doctest module frames from tracebacks and redundant newline character from a failure message.

  • gh-128840: Fix parsing long IPv6 addresses with embedded IPv4 address.

  • gh-134637: Fix performance regression in calling a ctypes function pointer in free threading.

  • gh-134696: Built-in HACL* and OpenSSL implementations of hash function constructors now correctly accept the same documented named arguments. For instance, md5() could be previously invoked as md5(data=data) or md5(string=string) depending on the underlying implementation but these calls were not compatible. Patch by Bénédikt Tran.

  • gh-134151: email: Fix TypeError in email.utils.decode_params() when sorting RFC 2231 continuations that contain an unnumbered section.

  • gh-134210: curses.window.getch() now correctly handles signals. Patch by Bénédikt Tran.

  • gh-134152: email: Fix parsing of email message ID with invalid domain.

  • gh-133489: random.getrandbits() can now generate more that 231 bits. random.randbytes() can now generate more that 256 MiB.

  • gh-132813: Improve error messages for incorrect types and values of csv.Dialect attributes.

  • gh-132969: Prevent the ProcessPoolExecutor executor thread, which remains running when shutdown(wait=False), from attempting to adjust the pool’s worker processes after the object state has already been reset during shutdown. A combination of conditions, including a worker process having terminated abormally, resulted in an exception and a potential hang when the still-running executor thread attempted to replace dead workers within the pool.

  • gh-127081: Fix libc thread safety issues with os by replacing getlogin with getlogin_r re-entrant version.

  • gh-131884: Fix formatting issues in json.dump() when both indent and skipkeys are used.

  • gh-130999: Avoid exiting the new REPL and offer suggestions even if there are non-string candidates when errors occur.

Documentation

  • gh-135171: Document that the iterator for the leftmost for clause in the generator expression is created immediately.

  • bpo-45210: Document that error indicator may be set in tp_dealloc, and how to avoid clobbering it.

Core and Builtins

  • gh-135496: Fix typo in the f-string conversion type error (“exclamanation” -> “exclamation”).

  • gh-135371: Fixed asyncio debugging tools to properly display internal coroutine call stacks alongside external task dependencies. The python -m asyncio ps and python -m asyncio pstree commands now show complete execution context. Patch by Pablo Galindo.

Library

  • gh-127319: Set the allow_reuse_port class variable to False on the XMLRPC, logging, and HTTP servers. This matches the behavior in prior Python releases, which is to not allow port reuse.

Core and Builtins

  • gh-135171: Reverts the behavior of async generator expressions when created with object w/o __aiter__ method to the pre-3.13 behavior of raising a TypeError.

  • gh-130077: Properly raise custom syntax errors when incorrect syntax containing names that are prefixes of soft keywords is encountered. Patch by Pablo Galindo.

  • gh-135171: Reverts the behavior of generator expressions when created with a non-iterable to the pre-3.13 behavior of raising a TypeError. It is no longer possible to cause a crash in the debugger by altering the generator expression’s local variables. This is achieved by moving the GET_ITER instruction back to the creation of the generator expression and adding an additional check to FOR_ITER.

Library

Core and Builtins

  • gh-134876: Add support to PEP 768 remote debugging for Linux kernels which don’t have CONFIG_CROSS_MEMORY_ATTACH configured.

  • gh-134889: Fix handling of a few opcodes that leave operands on the stack when optimizing LOAD_FAST.

Library

Core and Builtins

  • gh-132617: Fix dict.update() modification check that could incorrectly raise a “dict mutated during update” error when a different dictionary was modified that happens to share the same underlying keys object.

  • gh-134679: Fix crash in the free threading build’s QSBR code that could occur when changing an object’s __dict__ attribute.

  • gh-127682: No longer call __iter__ twice in list comprehensions. This brings the behavior of list comprehensions in line with other forms of iteration

  • gh-133912: Fix the C API function PyObject_GenericSetDict to handle extension classes with inline values.

C API

Build

  • gh-119132: Remove “experimental” tag from the CPython free-threading build.

  • gh-135497: Fix the detection of MAXLOGNAME in the configure.ac script.

  • gh-134923: Windows builds with profile-guided optimization enabled now use /GENPROFILE and /USEPROFILE instead of deprecated /LTCG: options.

  • gh-134774: Fix Py_DEBUG macro redefinition warnings on Windows debug builds. Patch by Chris Eibl.

  • gh-134632: Fixed build-details.json generation to use INCLUDEPY, in order to reference the pythonX.Y subdirectory of the include directory, as required in PEP 739, instead of the top-level include directory.

Python 3.14.0 beta 2

Release date: 2025-05-26

Windows

  • gh-130727: Fix a race in internal calls into WMI that can result in an “invalid handle” exception under high load. Patch by Chris Eibl.

  • gh-76023: Make os.path.realpath() ignore Windows error 1005 when in non-strict mode.

  • gh-133779: Reverts the change to generate different pyconfig.h files based on compiler settings, as it was frequently causing extension builds to break. In particular, the Py_GIL_DISABLED preprocessor variable must now always be defined explicitly when compiling for the experimental free-threaded runtime. The sysconfig.get_config_var() function can be used to determine whether the current runtime was compiled with that flag or not.

  • gh-133626: Ensures packages are not accidentally bundled into the traditional installer.

Tools/Demos

  • gh-134215: REPL import autocomplete only suggests private modules when explicitly specified.

Tests

  • gh-133744: Fix multiprocessing interrupt test. Add an event to synchronize the parent process with the child process: wait until the child process starts sleeping. Patch by Victor Stinner.

  • gh-133682: Fixed test case test.test_annotationlib.TestStringFormat.test_displays which ensures proper handling of complex data structures (lists, sets, dictionaries, and tuples) in string annotations.

  • gh-133639: Fix TestPyReplAutoindent.test_auto_indent_default() doesn’t run input_code.

Security

  • gh-133767: Fix use-after-free in the “unicode-escape” decoder with a non-“strict” error handler.

  • gh-128840: Short-circuit the processing of long IPv6 addresses early in ipaddress to prevent excessive memory consumption and a minor denial-of-service.

Library

Core and Builtins

  • gh-127960: PyREPL interactive shell no longer starts with __package__ and __file__ global names set to _pyrepl package internals. Contributed by Yuichiro Tachibana.

  • gh-130397: Remove special-casing for C stack depth limits for WASI. Due to WebAssembly’s built-in stack protection this does not pose a security concern.

  • gh-128066: Fixes an edge case where PyREPL improperly threw an error when Python is invoked on a read only filesystem while trying to write history file entries.

  • gh-69605: When auto-completing an import in the REPL, finding no candidates now issues no suggestion, rather than suggestions from the current namespace.

  • gh-134158: Fix coloring of double braces in f-strings and t-strings in the REPL.

  • gh-134119: Fix crash when calling next() on an exhausted template string iterator. Patch by Jelle Zijlstra.

  • gh-134100: Fix a use-after-free bug that occurs when an imported module isn’t in sys.modules after its initial import. Patch by Nico-Posada.

  • gh-133999: Fix SyntaxError regression in except parsing after gh-123440.

  • gh-133886: Fix sys.remote_exec() for non-ASCII paths in non-UTF-8 locales and non-UTF-8 paths in UTF-8 locales.

  • gh-133703: Fix hashtable in dict can be bigger than intended in some situations.

  • gh-133778: Fix bug where assigning to the __annotations__ attributes of classes defined under from __future__ import annotations had no effect.

  • gh-132762: fromkeys() no longer loops forever when adding a small set of keys to a large base dict. Patch by Angela Liss.

  • gh-133541: Inconsistent indentation in user input crashed the new REPL when syntax highlighting was active. This is now fixed.

  • gh-133516: Raise ValueError when constants True, False or None are used as an identifier after NFKC normalization.

  • gh-132542: Update Thread.native_id after fork(2) to ensure accuracy. Patch by Noam Cohen.

C API

Build

  • gh-134455: Fixed build-details.json generation to use the correct c_api.headers as defined in PEP 739, instead of c_api.include.

  • gh-131769: Fix detecting when the build Python in a cross-build is a pydebug build.

  • gh-117088: AIX linker don’t support -h option, so avoid it through platform check

Python 3.14.0 beta 1

Release date: 2025-05-06

Windows

Tools/Demos

  • gh-130453: Allow passing multiple keyword arguments with the same function name in pygettext.

  • gh-130195: Add warning messages when pygettext unimplemented -a/--extract-all option is called.

Tests

  • gh-133131: The iOS testbed will now select the most recently released “SE-class” device for testing if a device isn’t explicitly specified.

  • gh-91048: Add ability to externally inspect all pending asyncio tasks, even if no task is currently entered on the event loop.

  • gh-109981: The test helper that counts the list of open file descriptors now uses the optimised /dev/fd approach on all Apple platforms, not just macOS. This avoids crashes caused by guarded file descriptors.

  • gh-132678: Add --prioritize to -m test. This option allows the user to specify which selected tests should execute first, even if the order is otherwise randomized. This is particularly useful for tests that run the longest.

  • gh-131290: Tests in Lib/test can now be correctly executed as standalone scripts.

Security

  • gh-115322: The underlying extension modules behind readline:, subprocess, and ctypes now raise audit events on previously uncovered code paths that could lead to file system access related to C function calling and external binary execution. The ctypes.call_function audit hook has also been fixed to use an unsigned value for its function pointer.

Library

IDLE

  • gh-112936: fix IDLE: no Shell menu item in single-process mode.

Documentation

  • gh-107006: Move documentation and example code for threading.local from its docstring to the official docs.

  • gh-125142: As part of the builtin help intro text, show the keyboard shortcuts for the new, non-basic REPL (F1, F2, and F3).

Core and Builtins

  • gh-133336: -J is no longer reserved for use by Jython. Patch by Adam Turner.

  • gh-133261: Fix bug where the cycle GC could untrack objects in the trashcan because they looked like they were immortal. When objects are added to the trashcan, we take care to ensure they keep a mortal reference count.

  • gh-133346: Added experimental color theming support to the _colorize module.

  • gh-132917: For the free-threaded build, check the process memory usage increase before triggering a full automatic garbage collection. If the memory used has not increased 10% since the last collection then defer it.

  • gh-91048: Add a new python -m asyncio ps PID command-line interface to inspect asyncio tasks in a running Python process. Displays a flat table of await relationships. A variant showing a tree view is also available as python -m asyncio pstree PID. Both are useful for debugging async code. Patch by Pablo Galindo, Łukasz Langa, Yury Selivanov, and Marta Gomez Macias.

  • gh-133304: Workaround NaN’s “canonicalization” in PyFloat_Pack4() and PyFloat_Unpack4() on RISC-V.

  • gh-133197: Improve SyntaxError error messages for incompatible string / bytes prefixes.

  • gh-133231: Add new utilities of observing JIT compilation: sys._jit.is_available(), sys._jit.is_enabled(), and sys._jit.is_active().

Library

Core and Builtins

  • gh-131798: Split CALL_LEN into several uops allowing the JIT to remove them when optimizing. Patch by Diego Russo.

  • gh-131798: Use sym_new_type instead of sym_new_not_null for _BUILD_STRING, _BUILD_SET

  • gh-132942: Fix two races in the type lookup cache. This affected the free-threaded build and could cause crashes (apparently quite difficult to trigger).

  • gh-131798: Propagate the return type of _BINARY_OP_SUBSCR_TUPLE_INT in JIT. Patch by Tomas Roun

  • gh-132952: Speed up startup with the -S argument by importing the private _io module instead of io. This fixes a performance regression introduced earlier in Python 3.14 development and restores performance to the level of Python 3.13.

  • gh-131798: Allow the JIT to remove int guards after _CALL_LEN by setting the return type to int. Patch by Diego Russo

  • gh-131798: Split CALL_TUPLE_1 into several uops allowing the JIT to remove some of them. Patch by Tomas Roun

  • gh-131798: Split CALL_STR_1 into several uops allowing the JIT to remove some of them. Patch by Tomas Roun

  • gh-132825: Enhance unhashable key/element error messages for dict and set. Patch by Victor Stinner.

  • gh-131591: Reset any PEP 768 remote debugging pending call in children after os.fork() calls.

  • gh-132713: Fix repr(list) race condition: hold a strong reference to the item while calling repr(item). Patch by Victor Stinner.

  • gh-132661: Implement PEP 750 (Template Strings). Add new syntax for t-strings and implement new internal string.templatelib.Template and string.templatelib.Interpolation types.

  • gh-132479: Fix compiler crash in certain circumstances where multiple module-level annotations include comprehensions and other nested scopes.

  • gh-132747: Fix a crash when calling __get__() of a method with a None second argument.

  • gh-132744: Certain calls now check for runaway recursion and respect the system recursion limit.

  • gh-132449: Syntax errors that look like misspellings of Python keywords now provide a helpful fix suggestion for the typo. Contributed by Pablo Galindo Salgado.

Library

  • gh-132737: Support profiling code that requires __main__, such as pickle.

Core and Builtins

  • gh-132639: Added PyLong_AsNativeBytes(), PyLong_FromNativeBytes() and PyLong_FromUnsignedNativeBytes() to the limited C API.

  • gh-100239: Add specialisation for BINARY_OP/SUBSCR on list and slice.

  • gh-132508: Uses tagged integers on the evaluation stack to represent the instruction offsets when reraising an exception. This avoids the need to box the integer which could fail in low memory conditions.

  • gh-124476: Fix decoding from the locale encoding in the C.UTF-8 locale.

  • gh-131927: Compiler warnings originating from the same module and line number are now only emitted once, matching the behaviour of warnings emitted from user code. This can also be configured with warnings filters.

  • gh-132457: Make staticmethod() and classmethod() generic.

  • gh-131798: Use sym_new_type instead of sym_new_not_null for _BUILD_LIST, _BUILD_SET, _BUILD_MAP

  • gh-131798: Split CALL_TYPE_1 into several uops allowing the JIT to remove some of them.

  • gh-132386: Fix crash when passing a dict subclass as the globals parameter to exec().

  • gh-127682: No longer call __iter__ twice when creating and executing a generator expression. Creating a generator expression from a non-interable will raise only when the generator expression is executed. This brings the behavior of generator expressions in line with other generators.

  • gh-132261: The internal storage for annotations and annotate functions on classes now uses different keys in the class dictionary. This eliminates various edge cases where access to the __annotate__ and __annotations__ attributes would behave unpredictably.

  • gh-132284: Don’t wrap base PyCFunction slots on class creation if not overridden.

  • gh-130415: Improve the JIT’s ability to remove unused constant and local variable loads, and fix an issue where deallocating unused values could cause JIT code to crash or behave incorrectly.

  • gh-126703: Fix possible use after free in cases where a method’s definition has the same lifetime as its self.

  • gh-132286: Fix that type.__annotate__ was not deleted, when type.__annotations__ was deleted.

  • gh-131798: Allow the JIT to remove an extra _TO_BOOL_BOOL instruction after _CONTAINS_OP_DICT by setting the return type to bool.

  • gh-124715: Prevents against stack overflows when calling Py_DECREF(). Third-party extension objects no longer need to use the “trashcan” mechanism, as protection is now built into the Py_DECREF() macro.

  • gh-131798: Allow the JIT compiler to remove some type checks for operations on lists, tuples, dictionaries, and sets.

  • gh-128398: Improve error message when an object supporting the synchronous (resp. asynchronous) context manager protocol is entered using async with (resp. with) instead of with (resp. async with). Patch by Bénédikt Tran.

  • gh-131798: Allow the JIT to remove unicode guards after _BINARY_OP_SUBSCR_STR_INT by setting the return type to string.

  • gh-131878: Handle uncaught exceptions in the main input loop for the new REPL.

  • gh-131878: Fix support of unicode characters with two or more codepoints on Windows in the new REPL.

  • gh-126835: Move constant folding to the peephole optimizer. Rename AST optimization related files (Python/ast_opt.c -> Python/ast_preprocess.c), structs (_PyASTOptimizeState -> _PyASTPreprocessState) and functions (_PyAST_Optimize -> _PyAST_Preprocess, _PyCompile_AstOptimize -> _PyCompile_AstPreprocess).

  • gh-114809: Add support for macOS multi-arch builds with the JIT enabled

  • gh-131507: PyREPL now supports syntax highlighting. Contributed by Łukasz Langa.

  • gh-130907: If the __annotations__ of a module object are accessed while the module is executing, return the annotations that have been defined so far, without caching them.

  • gh-130104: Three-argument pow() now try calling __rpow__() if necessary. Previously it was only called in two-argument pow() and the binary power operator.

  • gh-130070: Fixed an assertion error for exec() passed a string source and a non-None closure. Patch by Bartosz Sławecki.

  • gh-129958: Fix a bug that was allowing newlines inconsistently in format specifiers for single-quoted f-strings. Patch by Pablo Galindo.

  • gh-129858: elif statements that follow an else block now have a specific error message.

  • gh-69605: Add module autocomplete to PyREPL.

  • gh-128555: Add the sys.flags.thread_inherit_context flag.

  • gh-123539: Improve SyntaxError message for using import ... as and from ... import ... as with not a name.

  • gh-102567: -X importtime now accepts value 2, which indicates that an importtime entry should also be printed if an imported module has already been loaded. Patch by Noah Kim and Adam Turner.

  • gh-116436: Improve error message when TypeError occurs during dict.update()

  • gh-103997: String arguments passed to “-c” are now automatically dedented as if by textwrap.dedent(). This allows “python -c” invocations to be indented in shell scripts without causing indentation errors. (Patch by Jon Crall and Steven Sun)

Library

  • gh-89562: Remove hostflags member from PySSLContext struct.

C API

Build

  • gh-113464: Use the cpython-bin-deps “externals” repository for Windows LLVM dependency management. Installing LLVM manually is no longer necessary for Windows JIT builds.

  • gh-133183: iOS compiler shims now include IPHONEOS_DEPLOYMENT_TARGET in target triples, ensuring that SDK version minimums are honored.

  • gh-133167: Fix compilation process with --enable-optimizations and --without-docstrings.

  • gh-133171: Since free-threaded builds do not support the experimental JIT compiler, prevent these configurations from being combined.

  • gh-132758: Fix building with tail call interpreter and pystats.

  • gh-132649: The PClayout script now allows passing --include-tcltk on Windows ARM64.

  • gh-132257: Change the default LTO flags on GCC to not pass -flto-partition=none, and allow parallelization of LTO. For newer GNU makes and GCC, this has a multiple factor speedup for LTO build times, with no noticeable loss in performance.

  • gh-132026: Fix use of undefined identifiers in platform triplet detection on MIPS Linux platforms.

Python 3.14.0 alpha 7

Release date: 2025-04-08

macOS

  • gh-124111: Update macOS installer to use Tcl/Tk 8.6.16.

  • gh-131423: Update macOS installer to use OpenSSL 3.0.16. Patch by Bénédikt Tran.

  • gh-131025: Update macOS installer to ship with SQLite 3.49.1.

Windows

  • gh-131423: Update bundled version of OpenSSL to 3.0.16. The new build also disables uplink support, which may be relevant to embedders but has no impact on normal use.

  • gh-131453: Some SND_* and MB_* constants are added to winsound.

  • gh-91349: Replaces our copy of zlib with zlib-ng, for performance improvements in zlib.

  • gh-131025: Update Windows installer to ship with SQLite 3.49.1.

Tools/Demos

  • gh-132121: Always escape non-printable Unicode characters in pygettext.

  • gh-131852: msgfmt no longer adds the POT-Creation-Date to generated .mo files for consistency with GNU msgfmt.

Tests

  • gh-131277: Allow to unset one or more environment variables at once via EnvironmentVarGuard.unset(). Patch by Bénédikt Tran.

  • gh-131050: test_ssl.test_dh_params is skipped if the underlying TLS library does not support finite-field ephemeral Diffie-Hellman.

Security

  • gh-131809: Update bundled libexpat to 2.7.1

  • gh-131261: Upgrade to libexpat 2.7.0

  • gh-121284: Fix bug in the folding of rfc2047 encoded-words when flattening an email message using a modern email policy. Previously when an encoded-word was too long for a line, it would be decoded, split across lines, and re-encoded. But commas and other special characters in the original text could be left unencoded and unquoted. This could theoretically be used to spoof header lines using a carefully constructed encoded-word if the resulting rendered email was transmitted or re-parsed.

Library

Documentation

Core and Builtins

  • gh-131798: Allow the JIT to remove an extra _TO_BOOL_BOOL instruction after _CONTAINS_OP_SET by setting the return type to bool.

  • gh-132011: Fix crash when calling list.append() as an unbound method.

  • gh-131998: Fix a crash when using an unbound method descriptor object in a function where a bound method descriptor was used.

  • gh-131591: Implement PEP 768 (Safe external debugger interface for CPython). Add a new sys.remote_exec() function to the sys module. This function schedules the execution of a Python file in a separate process. Patch by Pablo Galindo, Matt Wozniski and Ivona Stojanovic.

  • gh-131798: Allow JIT to omit str guard in truthiness test when str type is known.

  • gh-131833: Add support for optionally dropping grouping parentheses when using multiple exception types as per PEP 758. Patch by Pablo Galindo

  • gh-130924: Usage of a name in a function-scope annotation no longer triggers creation of a cell for that variable. This fixes a regression in earlier alphas of Python 3.14.

  • gh-131800: Improve the experimental JIT’s ability to remove type checks for certain subscripting operations.

  • gh-131738: Compiler emits optimized code for builtin any/all/tuple calls over a generator expression.

  • gh-131719: Fix missing NULL check in _PyMem_FreeDelayed in free-threaded build.

  • gh-131670: Fix anext() failing on sync __anext__() raising an exception.

  • gh-131666: Fix signature of anext_awaitable.close objects. Patch by Bénédikt Tran.

  • gh-130415: Optimize comparison of two constants in JIT builds

  • gh-129149: Add fast path for small and medium-size integers in PyLong_FromInt32(), PyLong_FromUInt32(), PyLong_FromInt64() and PyLong_FromUInt64(). Patch by Chris Eibl.

  • gh-130887: Optimize the AArch64 code generation for the JIT. Patch by Diego Russo

  • gh-130956: Optimize the AArch64 code generation for the JIT. Patch by Diego Russo

  • gh-130928: Fix error message when formatting bytes using the 'i' flag. Patch by Maxim Ageev.

  • gh-130935: Annotations at the class and module level that are conditionally defined are now only reflected in __annotations__ if the block they are in is executed. Patch by Jelle Zijlstra.

  • gh-130775: Do not crash on negative column and end_column in ast locations.

  • gh-130704: Optimize LOAD_FAST and its superinstruction form to reduce reference counting overhead. These instructions are replaced with faster variants that load borrowed references onto the operand stack when we can prove that the reference in the frame outlives the reference loaded onto the stack.

  • gh-88887: Fixing multiprocessing Resource Tracker process leaking, usually observed when running Python as PID 1.

  • gh-130115: Fix an issue with thread identifiers being sign-extended on some platforms.

Library

  • gh-99108: Add support for built-in implementation of HMAC (RFC 2104) based on HACL*. Patch by Bénédikt Tran.

Core and Builtins

  • gh-130080: Implement PEP 765: Disallow return/break/continue that exit a finally block.

  • gh-129900: Fix return codes inside SystemExit not getting returned by the REPL.

  • gh-128632: Disallow __classdict__ as the name of a type parameter. Using this name would previously crash the interpreter in some circumstances.

  • gh-126703: Improve performance of builtin methods by using a freelist.

  • gh-126703: Improve performance of range by using a freelist.

C API

  • gh-131740: Update PyUnstable_GC_VisitObjects to traverse perm gen.

  • gh-131525: The PyTupleObject now caches the computed hash value in the new field ob_hash.

Build

  • gh-131865: The DTrace build now properly passes the CC and CFLAGS variables to the dtrace command when utilizing SystemTap on Linux.

  • gh-131675: Fix mimalloc library builds for 32-bit ARM targets.

  • gh-131691: clang-cl on Windows needs option /EHa to support SEH (structured exception handling) correctly. Fix by Chris Eibl.

  • gh-131278: Add optimizing flag WITH_COMPUTED_GOTOS to Windows builds for when using a compiler that supports it (currently clang-cl). Patch by Chris Eibl.

  • gh-130213: Update the vendored HACL* library to fix build issues with older clang compilers.

  • gh-130673: Fix potential KeyError when handling object sections during JIT building process.

Python 3.14.0 alpha 6

Release date: 2025-03-14

macOS

Windows

  • gh-131020: pylauncher correctly detects a BOM when searching for the shebang. Fix by Chris Eibl.

Tools/Demos

  • gh-130453: Make it possible to override default keywords in pygettext.

  • gh-85012: Correctly reset msgctxt when compiling messages in msgfmt.

  • gh-130453: Extend support for specifying custom keywords in pygettext.

  • gh-130195: Add warning messages when pygettext unimplemented -a/--extract-all option is called.

  • gh-130057: Add support for translator comments in pygettext.py.

  • gh-130025: The iOS testbed now correctly handles symlinks used as Python framework references.

  • gh-129911: Fix the keyword entry in the help output of pygettext.

Tests

  • gh-129200: Multiple iOS testbed runners can now be started at the same time without introducing an ambiguity over simulator ownership.

  • gh-130292: The iOS testbed will now run successfully on a machine that has not previously run Xcode tests (such as CI configurations).

  • gh-130293: The tests of terminal colorization are no longer sensitive to the value of the TERM variable in the testing environment.

  • gh-129401: Fix a flaky test in test_repr_rlock that checks the representation of multiprocessing.RLock.

  • gh-126332: Add unit tests for pyrepl.

Security

  • gh-127371: Avoid unbounded buffering for tempfile.SpooledTemporaryFile.writelines(). Previously, disk spillover was only checked after the lines iterator had been exhausted. This is now done after each line is written.

Library

Documentation

Core and Builtins

  • gh-131141: Fix data race in sys.monitoring instrumentation while registering callback.

  • gh-130804: Fix support of unicode characters on Windows in the new REPL.

  • gh-130932: Fix incorrect exception handling in _PyModule_IsPossiblyShadowing

  • gh-122029: sys.setprofile() and sys.settrace() will not generate a c_call event for INSTRUMENTED_CALL_FUNCTION_EX if the callable is a method with a C function wrapped, because we do not generate c_return event in such case.

  • gh-129964: Fix JIT crash on Windows on Arm. Patch by Diego Russo and Brandt Bucher.

  • gh-130851: Fix a crash in the free threading build when constructing a code object with co_consts that contains instances of types that are not otherwise generated by the bytecode compiler.

  • gh-128534: Ensure that both left and right branches have the same source for async for loops. Add these branches to the co_branches() iterator.

  • gh-130794: Fix memory leak in the free threaded build when resizing a shared list or dictionary from multiple short-lived threads.

  • gh-130415: Improve JIT understanding of integers in boolean context.

  • gh-130382: Fix PyRefTracer_DESTROY not being sent from Python/ceval.c Py_DECREF().

  • gh-130574: Renumber RESUME from 149 to 128.

  • gh-124878: Fix race conditions during runtime finalization that could lead to accessing freed memory.

  • gh-130415: Improve the experimental JIT’s ability to narrow boolean values based on the results of truthiness tests.

  • gh-130618: Fix a bug that was causing UnicodeDecodeError or SystemError to be raised when using f-strings with lambda expressions with non-ASCII characters. Patch by Pablo Galindo

  • gh-123044: Make sure that the location of branch targets in match cases is in the body, not the pattern.

  • gh-128534: Add branch monitoring (BRANCH_LEFT and BRANCH_RIGHT events) for async for loops.

  • gh-130163: Fix possible crashes related to concurrent change and use of the sys module attributes.

  • gh-122029: INSTRUMENTED_CALL_KW will expand the method before monitoring to reflect the actual behavior more accurately.

  • gh-130415: Improve JIT’s ability to optimize strings in boolean contexts.

  • gh-130396: Use actual stack limits (from pthread_getattr_np(3)) for linux, and other systems with _GNU_SOURCE defined, when determining limits for C stack protection.

  • gh-128396: Fix a crash that occurs when calling locals() inside an inline comprehension that uses the same local variable as the outer frame scope where the variable is a free or cell var.

  • gh-129107: Fix two more bytearray functions for free threading.

  • gh-127705: Use tagged references (_PyStackRef) for the default build as well as for the free-threading build. This has a small negative performance impact short-term but will enable larger speedups in the future and significantly reduce maintenance costs by allowing a single implementation of tagged references in the future.

  • gh-130094: Fix two race conditions involving concurrent imports that could lead to spurious failures with ModuleNotFoundError.

  • gh-129107: Make bytearray iterator safe under free threading.

  • gh-115802: Use the more efficient “medium” code model for JIT-compiled code on supported platforms.

  • gh-107956: A build-details.json file is now install in the platform-independent standard library directory (PEP 739 implementation).

  • gh-116042: Fix location for SyntaxErrors of invalid escapes in the tokenizer. Patch by Pablo Galindo

  • gh-91079: Change C stack overflow protection to consider the amount of stack consumed, rather than a counter. This allows deeper recursion in many cases, but remains safe.

  • gh-129715: Improve the experimental JIT’s handling of returns to unknown callers.

Library

  • gh-129983: Fix data race in compile_template in sre.c.

Core and Builtins

  • gh-129967: Fix a race condition in the free threading build when repr(set) is called concurrently with set.clear().

  • gh-129953: The internal (evaluation) stack is now spilled to memory whenever execution escapes from the interpreter or JIT compiled code. This should have no observable effect in either Python or builtin extensions, but will allow various important optimizations in the future.

  • gh-129515: Clarify syntax error messages for conditional expressions when a statement is specified before an if or after an else keyword.

  • gh-129349: bytes.fromhex() and bytearray.fromhex() now accepts ASCII bytes and bytes-like objects.

  • gh-129149: Add fast path for medium-size integers in PyLong_FromSsize_t(). Patch by Chris Eibl.

  • gh-129107: Make the bytearray safe under free threading.

  • gh-128974: Fix a crash in UnicodeError.__str__ when custom attributes implement __str__() with side-effects. Patch by Bénédikt Tran.

  • gh-126085: typing.TypeAliasType now supports star unpacking.

  • gh-125331: from __future__ import barry_as_FLUFL now works in more contexts, including when it is used in files, with the -c flag, and in the REPL when there are multiple statements on the same line. Previously, it worked only on subsequent lines in the REPL, and when the appropriate flags were passed directly to compile(). Patch by Pablo Galindo.

  • gh-121464: Make concurrent iterations over the same enumerate() iterator safe under free-threading. See Strategy for Iterators in Free Threading.

  • gh-87790: Support underscore and comma as thousands separators in the fractional part for floating-point presentation types of the new-style string formatting (with format() or f-strings). Patch by Sergey B Kirpichev.

  • gh-124445: Fix specialization of generic aliases that are generic over a typing.ParamSpec and have been specialized with a nested type variable.

  • gh-120608: Adapt reversed() for use in the free-threading build. The reversed() is still not thread-safe in the sense that concurrent iterations may see the same object, but they will not corrupt the interpreter state.

Library

  • gh-100388: Fix the platform._sys_version() method when __DATE__ is undefined at buildtime by changing default buildtime datetime string to the UNIX epoch.

Core and Builtins

  • bpo-44369: Improve syntax errors for incorrectly closed strings. Patch by Pablo Galindo

C API

Build

  • gh-131035: Use -flto=thin for faster build times using clang-cl on Windows. Patch by Chris Eibl.

  • gh-130740: Ensure that Python.h is included before stdbool.h unless pyconfig.h is included before or in some platform-specific contexts.

  • gh-130090: Building with PlatformToolset=ClangCL on Windows now supports PGO (profile guided optimization). Patch by Chris Eibl with invaluable support from Steve Dover.

  • gh-129819: Allow building the JIT with the tailcall interpreter.

  • gh-129989: Fix a bug where the tailcall interpreter was enabled when --without-tail-call-interp was provided to the configure script.

  • gh-129838: Don’t redefine _Py_NO_SANITIZE_UNDEFINED when compiling with a recent GCC version and undefined sanitizer enabled.

  • gh-82909: #pragma-based linking with python3*.lib can now be switched off with Py_NO_LINK_LIB. Patch by Jean-Christophe Fillion-Robin.

Python 3.14.0 alpha 5

Release date: 2025-02-11

macOS

  • gh-91132: Update macOS installer to use ncurses 6.5.

Tools/Demos

  • gh-129248: The iOS test runner now strips the log prefix from each line output by the test suite.

  • gh-104400: Fix several bugs in extraction by switching to an AST parser in pygettext.

Tests

  • gh-129386: Add test.support.reset_code, which can be used to reset various bytecode-level optimizations and local instrumentation for a function.

  • gh-128474: Disable test_embed test cases that segfault on BOLT instrument binaries. The tests are only disabled when BOLT is enabled.

  • gh-128003: Add an option --parallel-threads=N to the regression test runner that runs individual tests in multiple threads in parallel in order to find concurrency bugs. Note that most of the test suite is not yet reviewed for thread-safety or annotated with @thread_unsafe when necessary.

Security

  • gh-105704: When using urllib.parse.urlsplit() and urllib.parse.urlparse() host parsing would not reject domain names containing square brackets ([ and ]). Square brackets are only valid for IPv6 and IPvFuture hosts according to RFC 3986 Section 3.2.2.

  • gh-126108: Fix a possible NULL pointer dereference in PySys_AddWarnOptionUnicode().

  • gh-80222: Fix bug in the folding of quoted strings when flattening an email message using a modern email policy. Previously when a quoted string was folded so that it spanned more than one line, the surrounding quotes and internal escapes would be omitted. This could theoretically be used to spoof header lines using a carefully constructed quoted string if the resulting rendered email was transmitted or re-parsed.

  • gh-119511: Fix a potential denial of service in the imaplib module. When connecting to a malicious server, it could cause an arbitrary amount of memory to be allocated. On many systems this is harmless as unused virtual memory is only a mapping, but if this hit a virtual address size limit it could lead to a MemoryError or other process crash. On unusual systems or builds where all allocated memory is touched and backed by actual ram or storage it could’ve consumed resources doing so until similarly crashing.

Library

IDLE

  • gh-129873: Simplify displaying the IDLE doc by only copying the text section of idle.html to idlelib/help.html. Patch by Stan Ulbrych.

Documentation

Core and Builtins

  • gh-100239: Replace the opcode BINARY_SUBSCR and its family by BINARY_OP with oparg NB_SUBSCR.

  • gh-129732: Fixed a race in _Py_qsbr_reserve in the free threading build.

  • gh-129763: Remove the internal LLTRACE macro (use Py_DEBUG instead).

  • gh-129715: Improve JIT performance for generators.

  • gh-129643: Fix thread safety of PyList_Insert() in free-threading builds.

  • gh-129668: Fix race condition when raising MemoryError in the free threaded build.

  • gh-129643: Fix thread safety of PyList_SetItem() in free-threading builds. Patch by Kumar Aditya.

  • gh-128563: Fix an issue where the “lltrace” debug feature could have been incorrectly enabled for some frames.

  • gh-129393: On FreeBSD, sys.platform doesn’t contain the major version anymore. It is always 'freebsd', instead of 'freebsd13' or 'freebsd14'.

Library

Core and Builtins

  • gh-129231: Improve memory layout of JIT traces. Patch by Diego Russo

  • gh-129149: Add fast path for medium-size integers in PyLong_FromUnsignedLong(), PyLong_FromUnsignedLongLong() and PyLong_FromSize_t().

  • gh-129201: The free-threaded version of the cyclic garbage collector has been optimized to conditionally use CPU prefetch instructions during the collection. This can reduce collection times by making it more likely that data is in the CPU cache when it is needed. The prefetch instructions are enabled if the number of long-lived objects (objects surviving a full collection) exceeds a threshold.

  • gh-129093: Fix f-strings such as f'{expr=}' sometimes not displaying the full expression when the expression contains !=.

  • gh-124363: Treat debug expressions in f-string as raw strings. Patch by Pablo Galindo

  • gh-128714: Fix the potential races in get/set dunder methods __annotations__, __annotate__ and __type_params__ for function object, and add related tests.

  • gh-128799: Add frame of except* to traceback when it wraps a naked exception.

  • gh-128842: Collect JIT memory stats using pystats. Patch by Diego Russo.

  • gh-100239: Specialize BINARY_OP for bitwise logical operations on compact ints.

  • gh-128910: Undocumented and unused private C-API functions _PyTrash_begin and _PyTrash_end are removed.

  • gh-128807: Add a marking phase to the free-threaded GC. This is similar to what was done in gh-126491. Since the free-threaded GC does not have generations and is not incremental, the marking phase looks for all objects reachable from known roots. The roots are objects known to not be garbage, like the module dictionary for sys. For most programs, this marking phase should make the GC a bit faster since typically less work is done per object.

  • gh-100239: Add opcode BINARY_OP_EXTEND which executes a pair of functions (guard and specialization functions) accessed from the inline cache.

  • gh-128563: A new type of interpreter has been added to CPython. This interpreter uses tail calls for its instruction handlers. Preliminary benchmark results suggest 7-11% geometric mean faster on pyperformance (depending on platform), and up to 30% faster on Python-intensive workloads. This interpreter currently only works on newer compilers, such as clang-19. Other compilers will continue using the old interpreter. Patch by Ken Jin, with ideas on how to implement this in CPython by Mark Shannon, Garret Gu, Haoran Xu, and Josh Haberman.

  • gh-126703: Improve performance of iterating over lists and tuples by using a freelist for the iterator objects.

  • gh-127953: The time to handle a LINE event in sys.monitoring (and sys.settrace) is now independent of the number of lines in the code object.

  • gh-128330: Restore terminal control characters on REPL exit.

  • gh-128016: Improved the SyntaxWarning message for invalid escape sequences to clarify that such sequences will raise a SyntaxError in future Python releases. The new message also suggests a potential fix, i.e., Did you mean "\\e"?.

  • gh-126004: Fix handling of UnicodeError.start and UnicodeError.end values in the codecs.replace_errors() error handler. Patch by Bénédikt Tran.

  • gh-126004: Fix handling of UnicodeError.start and UnicodeError.end values in the codecs.backslashreplace_errors() error handler. Patch by Bénédikt Tran.

  • gh-126004: Fix handling of UnicodeError.start and UnicodeError.end values in the codecs.xmlcharrefreplace_errors() error handler. Patch by Bénédikt Tran.

  • gh-127119: Slightly optimize the int deallocator.

  • gh-127349: Fixed the error when resizing terminal in Python REPL. Patch by Semyon Moroz.

  • gh-125723: Fix crash with gi_frame.f_locals when generator frames outlive their generator. Patch by Mikhail Efimov.

Library

Core and Builtins

  • gh-115911: If the current working directory cannot be determined due to permissions, then import will no longer raise PermissionError. Patch by Alex Willmer.

Library

C API

Build

  • gh-129660: Drop test_embed from PGO training, whose contribution in recent versions is considered to be ignorable.

  • gh-128902: Fix compile errors with Clang 9 and older due to lack of __attribute__((fallthrough)) support.

Python 3.14.0 alpha 4

Release date: 2025-01-14

macOS

  • gh-127592: Usage of the unified Apple System Log APIs was disabled when the minimum macOS version is earlier than 10.12.

Tools/Demos

  • gh-128152: Fix a bug where Argument Clinic’s C pre-processor parser tried to parse pre-processor directives inside C comments. Patch by Erlend Aasland.

Tests

  • gh-128690: Temporarily do not use test_embed in PGO profile builds until the problem with test_init_pyvenv_cfg failing in some configurations is resolved.

Library

Core and Builtins

  • gh-128078: Fix a SystemError when using anext() with a default tuple value. Patch by Bénédikt Tran.

  • gh-128717: Fix a crash when setting the recursion limit while other threads are active on the free threaded build.

  • gh-124483: Treat Py_DECREF and variants as escaping when generating opcode and uop metadata. This prevents the possibility of a __del__ method causing the JIT to behave incorrectly.

  • gh-126703: Improve performance of class methods by using a freelist.

  • gh-128137: Update PyASCIIObject layout to handle interned field with the atomic operation. Patch by Donghee Na.

Library

Core and Builtins

  • gh-126868: Increase usage of freelist for int allocation.

  • gh-114203: Optimize Py_BEGIN_CRITICAL_SECTION for simple recursive calls.

  • gh-127705: Adds stackref debugging when Py_STACKREF_DEBUG is set. Finds all double-closes and leaks, logging the origin and last borrow.

    Inspired by HPy’s debug mode. https://docs.hpyproject.org/en/latest/debug-mode.html

  • gh-128079: Fix a bug where except* does not properly check the return value of an ExceptionGroup’s split() function, leading to a crash in some cases. Now when split() returns an invalid object, except* raises a TypeError with the original raised ExceptionGroup object chained to it.

  • gh-128030: Avoid error from calling PyModule_GetFilenameObject on a non-module object when importing a non-existent symbol from a non-module object.

Library

  • gh-128035: Indicate through ssl.HAS_PHA whether the ssl module supports TLSv1.3 post-handshake client authentication (PHA). Patch by Will Childs-Klein.

Core and Builtins

  • gh-127274: Add a new flag, CO_METHOD, to co_flags that indicates whether the code object belongs to a function defined in class scope.

  • gh-66409: During the path initialization, we now check if base_exec_prefix is the same as base_prefix before falling back to searching the Python interpreter directory.

  • gh-127970: We now use the location of the libpython runtime library used in the current process to determine sys.base_prefix on all platforms implementing the dladdr function defined by the UNIX standard — this includes Linux, Android, macOS, iOS, FreeBSD, etc. This was already the case on Windows and macOS Framework builds.

  • gh-127773: Do not use the type attribute cache for types with incompatible MRO.

  • gh-127903: Objects/unicodeobject.c: fix a crash on DEBUG builds in _copy_characters when there is nothing to copy.

  • gh-127809: Fix an issue where the experimental JIT may infer an incorrect result type for exponentiation (** and **=), leading to bugs or crashes.

  • gh-126862: Fix a possible overflow when a class inherits from an absurd number of super-classes. Reported by Valery Fedorenko. Patch by Bénédikt Tran.

C API

Build

  • gh-128627: For Emscripten builds the function pointer cast call trampoline now uses the wasm-gc ref.test instruction if it’s available instead of Wasm JS type reflection.

  • gh-128472: Skip BOLT optimization of functions using computed gotos, fixing errors on build with LLVM 19.

  • gh-115765: GNU Autoconf 2.72 is now required to generate configure. Patch by Erlend Aasland.

  • gh-123925: Fix building the curses module on platforms with libncurses but without libncursesw.

  • gh-90905: Add support for cross-compiling to x86_64 on aarch64/arm64 macOS.

  • gh-128321: Set LIBS instead of LDFLAGS when checking if sqlite3 library functions are available. This fixes the ordering of linked libraries during checks, which was incorrect when using a statically linked libsqlite3.

  • gh-100384: Error on unguarded-availability in macOS builds, preventing invalid use of symbols that are not available in older versions of the OS.

  • gh-128104: Remove Py_STRFTIME_C99_SUPPORT conditions in favor of requiring C99 strftime(3) specifier support at build time. When cross-compiling, there is no build time check and support is assumed.

  • gh-127951: Add option --pystats to the Windows build to enable performance statistics collection.

Python 3.14.0 alpha 3

Release date: 2024-12-17

Windows

  • gh-127353: Allow to force color output on Windows using environment variables. Patch by Andrey Efremov.

  • gh-125729: Makes the presence of the turtle module dependent on the Tcl/Tk installer option. Previously, the module was always installed but would be unusable without Tcl/Tk.

Tools/Demos

Tests

  • gh-127906: Test the limited C API in test_cppext. Patch by Victor Stinner.

  • gh-127637: Add tests for the dis command-line interface. Patch by Bénédikt Tran.

  • gh-126925: iOS test results are now streamed during test execution, and the deprecated xcresulttool is no longer used.

  • gh-127076: Disable strace based system call tests when LD_PRELOAD is set.

  • gh-127076: Filter out memory-related mmap, munmap, and mprotect calls from file-related ones when testing io behavior using strace.

Security

Library

Documentation

Core and Builtins

  • gh-127740: Fix error message in bytes.fromhex() when given an odd number of digits to properly indicate that an even number of hexadecimal digits is required.

  • gh-127058: PySequence_Tuple now creates the resulting tuple atomically, preventing partially created tuples being visible to the garbage collector or through gc.get_referrers()

  • gh-127599: Fix statistics for increments of object reference counts (in particular, when a reference count was increased by more than 1 in a single operation).

  • gh-127651: When raising ImportError for missing symbols in from imports, use __file__ in the error message if __spec__.origin is not a location

  • gh-127582: Fix non-thread-safe object resurrection when calling finalizers and watcher callbacks in the free threading build.

  • gh-127434: The iOS compiler shims can now accept arguments with spaces.

  • gh-127536: Add missing locks around some list assignment operations in the free threading build.

  • gh-127085: Fix race when exporting a buffer from a memoryview object on the free-threaded build.

  • gh-127238: Correct error message for sys.set_int_max_str_digits().

  • gh-113841: Fix possible undefined behavior division by zero in complex’s _Py_c_pow().

Library

Core and Builtins

  • gh-126491: Add a marking phase to the GC. All objects that can be transitively reached from builtin modules or the stacks are marked as reachable before cycle detection. This reduces the amount of work done by the GC by approximately half.

  • gh-127020: Fix a crash in the free threading build when PyCode_GetCode(), PyCode_GetVarnames(), PyCode_GetCellvars(), or PyCode_GetFreevars() were called from multiple threads at the same time.

  • gh-127010: Simplify GC tracking of dictionaries. All dictionaries are tracked when created, rather than being lazily tracked when a trackable object was added to them. This simplifies the code considerably and results in a slight speedup.

  • gh-126980: Fix __buffer__() of bytearray crashing when READ or WRITE are passed as flags.

  • gh-126937: Fix TypeError when a ctypes.Structure has a field size that doesn’t fit into an unsigned 16-bit integer. Instead, the maximum number of bits is sys.maxsize.

  • gh-126868: Increase performance of int by adding a freelist for compact ints.

  • gh-126881: Fix crash in finalization of dtoa state. Patch by Kumar Aditya.

  • gh-126892: Require cold or invalidated code to “warm up” before being JIT compiled again.

  • gh-126091: Ensure stack traces are complete when throwing into a generator chain that ends in a custom generator.

  • gh-126024: Optimize decoding of short UTF-8 sequences containing non-ASCII characters by approximately 15%.

  • gh-125420: Add memoryview.index() to memoryview objects. Patch by Bénédikt Tran.

  • gh-125420: Add memoryview.count() to memoryview objects. Patch by Bénédikt Tran.

  • gh-124470: Fix crash in free-threaded builds when replacing object dictionary while reading attribute on another thread

  • gh-69639: Implement mixed-mode arithmetic rules combining real and complex numbers as specified by C standards since C99. Patch by Sergey B Kirpichev.

  • gh-120010: Correct invalid corner cases which resulted in (nan+nanj) output in complex multiplication, e.g., (1e300+1j)*(nan+infj). Patch by Sergey B Kirpichev.

  • gh-109746: If _thread.start_new_thread() fails to start a new thread, it deletes its state from interpreter and thus avoids its repeated cleanup on finalization.

C API

Build

  • gh-127865: Fix build failure on systems without thread-locals support.

  • gh-127629: Emscripten builds now include ctypes support.

  • gh-127111: Updated the Emscripten web example to use ES6 modules and be built into a distinct web_example subfolder.

  • gh-115869: Make jit_stencils.h (which is produced during JIT builds) reproducible.

  • gh-126898: The Emscripten build of Python is now based on ES6 modules.

Python 3.14.0 alpha 2

Release date: 2024-11-19

Windows

  • gh-126911: Update credits command output.

  • gh-118973: Ensures the experimental free-threaded install includes the _tkinter module. The optional Tcl/Tk component must also be installed in order for the module to work.

  • gh-126497: Fixes venv failure due to missing redirector executables in experimental free-threaded installs.

  • gh-126074: Removed unnecessary DLLs from Windows embeddable package

  • gh-125315: Avoid crashing in platform due to slow WMI calls on some Windows machines.

  • gh-126084: Fix venvwlauncher to launch pythonw instead of python so no extra console window is created.

  • gh-125842: Fix a SystemError when sys.exit() is called with 0xffffffff on Windows.

  • gh-125550: Enable the Python install manager to detect Python 3.14 installs from the Windows Store.

  • gh-123803: All Windows code pages are now supported as “cpXXX” codecs on Windows.

Tools/Demos

  • gh-126807: Fix extraction warnings in pygettext.py caused by mistaking function definitions for function calls.

  • gh-126167: The iOS testbed was modified so that it can be used by third-party projects for testing purposes.

Tests

  • gh-126909: Fix test_os extended attribute tests to work on filesystems with 1 KiB xattr size limit.

  • gh-125730: Change make test to not run GUI tests by default. Use make ci to run tests with GUI tests instead.

  • gh-124295: Add translation tests to the argparse module.

Security

Library

Documentation

  • gh-126622: Added stub pages for removed modules explaining their removal, where to find replacements, and linking to the last Python version that supported them. Contributed by Ned Batchelder.

  • gh-125277: Require Sphinx 7.2.6 or later to build the Python documentation. Patch by Adam Turner.

  • gh-60712: Include the object type in the lists of documented types. Change by Furkan Onder and Martin Panter.

Core and Builtins

  • gh-126795: Increase the threshold for JIT code warmup. Depending on platform and workload, this can result in performance gains of 1-9% and memory savings of 3-5%.

  • gh-126341: Now ValueError is raised instead of SystemError when trying to iterate over a released memoryview object.

  • gh-126688: Fix a crash when calling os.fork() on some operating systems, including SerenityOS.

Library

  • gh-126066: Fix importlib to not write an incomplete .pyc files when a ulimit or some other operating system mechanism is preventing the write to go through fully.

Core and Builtins

  • gh-126222: Do not include count of “peek” items in _PyUop_num_popped. This ensures that the correct number of items are popped from the stack when a micro-op exits with an error.

  • gh-126366: Fix crash when using yield from on an object that raises an exception in its __iter__.

Library

  • gh-126209: Fix an issue with skip_file_prefixes parameter which resulted in an inconsistent behaviour between the C and Python implementations of warnings.warn(). Patch by Daehee Kim.

Core and Builtins

  • gh-126312: Fix crash during garbage collection on an object frozen by gc.freeze() on the free-threaded build.

  • gh-103951: Relax optimization requirements to allow fast attribute access to module subclasses.

  • gh-126072: Following gh-126101, for Code Objects like lambda, annotation and type alias, we no longer add None to its co_consts.

  • gh-126195: Improve JIT performance by 1.4% on macOS Apple Silicon by using platform-specific memory protection APIs. Patch by Diego Russo.

  • gh-126139: Provide better error location when attempting to use a future statement with an unknown future feature.

  • gh-126072: Add a new attribute in co_flags to indicate whether the first item in co_consts is the docstring. If a code object has no docstring, None will NOT be inserted.

  • gh-126076: Relocated objects such as tuple, bytes and str objects are properly tracked by tracemalloc and its associated hooks. Patch by Pablo Galindo.

  • gh-90370: Avoid temporary tuple creation for vararg in argument passing with Argument Clinic generated code (if arguments either vararg or positional-only).

  • gh-126018: Fix a crash in sys.audit() when passing a non-string as first argument and Python was compiled in debug mode.

  • gh-126012: The memoryview type now supports subscription, making it a generic type.

  • gh-125837: Adds LOAD_SMALL_INT and LOAD_CONST_IMMORTAL instructions. LOAD_SMALL_INT pushes a small integer equal to the oparg to the stack. LOAD_CONST_IMMORTAL does the same as LOAD_CONST but is more efficient for immortal objects. Removes RETURN_CONST instruction.

  • gh-125942: On Android, the errors setting of sys.stdout was changed from surrogateescape to backslashreplace.

  • gh-125859: Fix a crash in the free threading build when gc.get_objects() or gc.get_referrers() is called during an in-progress garbage collection.

  • gh-125868: It was possible in 3.14.0a1 only for attribute lookup to give the wrong value. This was due to an incorrect specialization in very specific circumstances. This is fixed in 3.14.0a2.

  • gh-125498: The JIT has been updated to leverage Clang 19’s new preserve_none attribute, which supports more platforms and is more useful than LLVM’s existing ghccc calling convention. This also removes the need to manually patch the calling convention in LLVM IR, simplifying the JIT compilation process.

  • gh-125703: Correctly honour tracemalloc hooks in specialized Py_DECREF paths. Patch by Pablo Galindo

  • gh-125593: Use color to highlight error locations in traceback from exception group

  • gh-125017: Fix crash on certain accesses to the __annotations__ of staticmethod and classmethod objects.

  • gh-125588: The Python PEG generator can now use f-strings in the grammar actions. Patch by Pablo Galindo

  • gh-125444: Fix illegal instruction for older Arm architectures. Patch by Diego Russo, testing by Ross Burton.

  • gh-118423: Add a new INSTRUCTION_SIZE macro to the cases generator which returns the current instruction size.

  • gh-125038: Fix crash when iterating over a generator expression after direct changes on gi_frame.f_locals. Patch by Mikhail Efimov.

  • gh-124855: Don’t allow the JIT and perf support to be active at the same time. Patch by Pablo Galindo

  • gh-123714: Update JIT compilation to use LLVM 19

  • gh-123930: Improve the error message when a script shadowing a module from the standard library causes ImportError to be raised during a “from” import. Similarly, improve the error message when a script shadowing a third party module attempts to “from” import an attribute from that third party module while still initialising.

  • gh-119793: The map() built-in now has an optional keyword-only strict flag like zip() to check that all the iterables are of equal length. Patch by Wannes Boeykens.

Library

  • gh-118950: Fix bug where SSLProtocol.connection_lost wasn’t getting called when OSError was thrown on writing to socket.

  • gh-113570: Fixed a bug in reprlib.repr where it incorrectly called the repr method on shadowed Python built-in types.

C API

Build

  • gh-126691: Removed the --with-emscripten-target configure flag. We unified the node and browser options and the same build can now be used, independent of target runtime.

  • gh-123877: Use wasm32-wasip1 as the target triple for WASI instead of wasm32-wasi. The latter will eventually be reclaimed for WASI 1.0 while CPython currently only supports WASI preview1.

  • gh-126458: Disable SIMD support for HACL under WASI.

  • gh-89640: Hard-code float word ordering as little endian on WASM.

  • gh-126206: make clinic now runs Argument Clinic using the --force option, thus forcefully regenerating generated code.

  • gh-126187: Introduced Tools/wasm/emscripten.py to simplify doing Emscripten builds.

  • gh-124932: For cross builds, there is now support for having a different install prefix than the host_prefix used by getpath.py. This is set to / by default for Emscripten, on other platforms the default behavior is the same as before.

  • gh-125946: The minimum supported Android version is now 7.0 (API level 24).

  • gh-125940: The Android build now supports 16 KB page sizes.

  • gh-89640: Improve detection of float word ordering on Linux when link-time optimizations are enabled.

  • gh-124928: Emscripten builds now require node >= 18.

  • gh-115382: Fix cross compile failures when the host and target SOABIs match.

Python 3.14.0 alpha 1

Release date: 2024-10-15

macOS

  • gh-124448: Update bundled Tcl/Tk in macOS installer to 8.6.15.

  • gh-123797: Check for runtime availability of ptsname_r function on macos.

  • gh-123418: Updated macOS installer build to use OpenSSL 3.0.15.

Windows

  • gh-124487: Increases Windows required OS and API level to Windows 10.

  • gh-124609: Fix _Py_ThreadId for Windows builds using MinGW. Patch by Tony Roberts.

  • gh-124448: Updated bundled Tcl/Tk to 8.6.15.

  • gh-124254: Ensures experimental free-threaded binaries remain installed when updating.

  • gh-123915: Ensure that Tools\msi\buildrelease.bat uses different directories for AMD64 and ARM64 builds.

  • gh-123418: Updated Windows build to use OpenSSL 3.0.15.

  • gh-123476: Add support for socket.TCP_QUICKACK on Windows platforms.

  • gh-122573: The Windows build of CPython now requires 3.10 or newer.

  • gh-100256: mimetypes no longer fails when it encounters an inaccessible registry key.

  • gh-119679: Ensures correct import libraries are included in Windows installs.

  • gh-119690: Adds Unicode support and fixes audit events for _winapi.CreateNamedPipe.

  • gh-111201: Add support for new pyrepl on Windows

  • gh-119070: Fixes py.exe handling of shebangs like /usr/bin/env python3.12, which were previously interpreted as python3.exe instead of python3.12.exe.

  • gh-117505: Fixes an issue with the Windows installer not running ensurepip in a fully isolated environment. This could cause unexpected interactions with the user site-packages.

  • gh-118209: Avoid crashing in mmap on Windows when the mapped memory is inaccessible due to file system errors or access violations.

  • gh-79846: Makes ssl.create_default_context() ignore invalid certificates in the Windows certificate store

Tools/Demos

  • gh-123418: Update GitHub CI workflows to use OpenSSL 3.0.15 and multissltests to use 3.0.15, 3.1.7, and 3.2.3.

Tests

  • gh-125041: Re-enable skipped tests for zlib on the s390x architecture: only skip checks of the compressed bytes, which can be different between zlib’s software implementation and the hardware-accelerated implementation.

  • gh-124378: Updated test_ttk to pass with Tcl/Tk 8.6.15.

  • gh-124213: Detect whether the test suite is running inside a systemd-nspawn container with --suppress-sync=true option, and skip the test_os and test_mmap tests that are failing in this scenario.

  • gh-124190: Add capability to ignore entire files or directories in check warning CI tool

  • gh-121921: Update Lib/test/crashers/bogus_code_obj.py so that it crashes properly again.

  • gh-112301: Add tooling to check for changes in compiler warnings. Patch by Nate Ohlson.

  • gh-59022: Add tests for pkgutil.extend_path(). Patch by Andreas Stocker.

  • gh-99242: os.getloadavg() may throw OSError when running regression tests under certain conditions (e.g. chroot). This error is now caught and ignored, since reporting load average is optional.

  • gh-121084: Fix test_typing random leaks. Clear typing ABC caches when running tests for refleaks (-R option): call _abc_caches_clear() on typing abstract classes and their subclasses. Patch by Victor Stinner.

  • gh-121160: Add a test for readline.set_history_length(). Note that this test may fail on readline libraries.

  • gh-121200: Fix test_expanduser_pwd2() of test_posixpath. Call getpwnam() to get pw_dir, since it can be different than getpwall() pw_dir. Patch by Victor Stinner.

  • gh-121188: When creating the JUnit XML file, regrtest now escapes characters which are invalid in XML, such as the chr(27) control character used in ANSI escape sequences. Patch by Victor Stinner.

  • gh-120801: Cleaned up fixtures for importlib.metadata tests and consolidated behavior with ‘test.support.os_helper’.

  • gh-119727: Add --single-process command line option to Python test runner (regrtest). Patch by Victor Stinner.

  • gh-119273: Python test runner no longer runs tests using TTY (ex: test_ioctl) in a process group (using setsid()). Previously, tests using TTY were skipped. Patch by Victor Stinner.

  • gh-119050: regrtest test runner: Add XML support to the refleak checker (-R option). Patch by Victor Stinner.

  • gh-101525: Skip test_gdb if the binary is relocated by BOLT. Patch by Donghee Na.

  • gh-107562: Test certificates have been updated to expire far in the future. This allows testing Y2038 with system time set to after that, so that actual Y2038 issues can be exposed, and not masked by expired certificate errors.

Security

  • gh-125140: Remove the current directory from sys.path when using PyREPL.

  • gh-123678: Upgrade libexpat to 2.6.3

  • gh-112301: Enable compiler options that warn of potential security vulnerabilities.

  • gh-122792: Changed IPv4-mapped ipaddress.IPv6Address to consistently use the mapped IPv4 address value for deciding properties. Properties which have their behavior fixed are is_multicast, is_reserved, is_link_local, is_global, and is_unspecified.

  • gh-112301: Add ability to ignore warnings per file with warning count in warning checking tooling. Patch by Nate Ohlson.

  • gh-112301: Add macOS warning tracking to warning check tooling. Patch by Nate Ohlson.

  • gh-122133: Authenticate the socket connection for the socket.socketpair() fallback on platforms where AF_UNIX is not available like Windows.

    Patch by Gregory P. Smith <greg@krypto.org> and Seth Larson <seth@python.org>. Reported by Ellie <el@horse64.org>

  • gh-121957: Fixed missing audit events around interactive use of Python, now also properly firing for python -i, as well as for python -m asyncio. The events in question are cpython.run_stdin and cpython.run_startup.

  • gh-112301: Enable runtime protections for glibc to abort execution when unsafe behavior is encountered, for all platforms except Windows.

  • gh-121285: Remove backtracking from tarfile header parsing for hdrcharset, PAX, and GNU sparse headers.

  • gh-112301: Add default compiler options to improve security. Enable -Wimplicit-fallthrough, -fstack-protector-strong, -Wtrampolines.

  • gh-118773: Fixes creation of ACLs in os.mkdir() on Windows to work correctly on non-English machines.

  • gh-118486: os.mkdir() on Windows now accepts mode of 0o700 to restrict the new directory to the current user. This fixes CVE 2024-4030 affecting tempfile.mkdtemp() in scenarios where the base temporary directory is more permissive than the default.

Library

IDLE

  • gh-122392: Increase currently inadequate vertical spacing for the IDLE browsers (path, module, and stack) on high-resolution monitors.

  • gh-112938: Fix uninteruptable hang when Shell gets rapid continuous output.

  • gh-122482: Change About IDLE to direct users to discuss.python.org instead of the now unused idle-dev email and mailing list.

  • gh-78889: Stop Shell freezes by blocking user access to non-method sys.stdout.shell attributes, which are all private.

  • gh-120083: Add explicit black IDLE Hovertip foreground color needed for recent macOS. Fixes Sonoma showing unreadable white on pale yellow. Patch by John Riggles.

  • gh-120104: Fix padding in config and search dialog windows in IDLE.

Documentation

  • gh-124872: Added definitions for context, current context, and context management protocol, updated related definitions to be consistent, and expanded the documentation for contextvars.Context.

  • gh-125018: The importlib.metadata documentation now includes semantic cross-reference targets for the significant documented APIs. This means intersphinx references like importlib.metadata.version() will now work as expected.

  • gh-124720: Update “Using Python on a Mac” section of the “Python Setup and Usage” document and include information on installing free-threading support.

  • gh-124457: Remove coverity scan from the CPython repo. It has not been used since 2020 and is currently unmaintained.

  • gh-116622: Add an Android platform guide, and flag modules not available on Android.

  • gh-123976: Refresh docs around custom providers.

  • gh-70870: Clarified the dual usage of the term “free variable” (both the formal meaning of any reference to names defined outside the local scope, and the narrower pragmatic meaning of nonlocal variables named in co_freevars).

  • gh-121277: Writers of CPython’s documentation can now use next as the version for the versionchanged, versionadded, deprecated directives.

  • gh-117765: Improved documentation for unittest.mock.patch.dict()

  • gh-121749: Fix documentation for PyModule_AddObjectRef().

  • gh-120012: Clarify the behaviours of multiprocessing.Queue.empty() and multiprocessing.SimpleQueue.empty() on closed queues. Patch by Bénédikt Tran.

  • gh-119574: Added some missing environment variables to the output of --help-env.

  • bpo-34008: The Py_Main() documentation moved from the “Very High Level API” section to the “Initialization and Finalization” section.

    Also make it explicit that we expect Py_Main to typically be called instead of Py_Initialize rather than after it (since Py_Main makes its own call to Py_Initialize). Document that calling both is supported but is version dependent on which settings will be applied correctly.

Core and Builtins

  • gh-124375: Fix a crash in the free threading build when the GC runs concurrently with a new thread starting.

  • gh-125221: Fix possible race condition when calling __reduce_ex__() for the first time in the free threading build.

  • gh-125174: Make the handling of reference counts of immortal objects more robust. Immortal objects with reference counts that deviate from their original reference count by up to a billion (half a billion on 32 bit builds) are still counted as immortal.

  • gh-125039: Make this_instr and prev_instr const in cases generator.

Library

Core and Builtins

  • gh-124871: Fix compiler bug (in some versions of 3.13) where an assertion fails during reachability analysis.

  • gh-123378: Fix a crash in the __str__() method of UnicodeError objects when the UnicodeError.start and UnicodeError.end values are invalid or out-of-range. Patch by Bénédikt Tran.

  • gh-118093: Improve the experimental JIT compiler’s ability to stay “on trace” when encountering highly-biased branches.

  • gh-124642: Fixed scalability issue in free-threaded builds for lock-free reads from dictionaries in multi-threaded scenarios

  • gh-116510: Fix a crash caused by immortal interned strings being shared between sub-interpreters that use basic single-phase init. In that case, the string can be used by an interpreter that outlives the interpreter that created and interned it. For interpreters that share obmalloc state, also share the interned dict with the main interpreter.

  • gh-116510: Fix a bug that can cause a crash when sub-interpreters use “basic” single-phase extension modules. Shared objects could refer to PyGC_Head nodes that had been freed as part of interpreter cleanup.

  • gh-119180: The __main__ module no longer always contains an __annotations__ dictionary in its global namespace.

  • gh-124547: When deallocating an object with inline values whose __dict__ is still live: if memory allocation for the inline values fails, clear the dictionary. Prevents an interpreter crash.

  • gh-124513: Fix a crash in FrameLocalsProxy constructor: check the number of arguments. Patch by Victor Stinner.

  • gh-124442: Fix nondeterminism in compilation by sorting the value of __static_attributes__. Patch by kp2pml30.

  • gh-124285: Fix bug where bool(a) can be invoked more than once during the evaluation of a compound boolean expression.

  • gh-123856: Fix PyREPL failure when a keyboard interrupt is triggered after using a history search

  • gh-65961: Deprecate the setting and using __package__ and __cached__.

  • gh-119726: The JIT now generates more efficient code for calls to C functions resulting in up to 0.8% memory savings and 1.5% speed improvement on AArch64. Patch by Diego Russo.

  • gh-122878: Use the pager binary, if available (e.g. on Debian and derivatives), to display REPL help().

  • gh-124188: Fix reading and decoding a line from the source file with non-UTF-8 encoding for syntax errors raised in the compiler.

  • gh-124027: Support <page up>, <page down>, and <delete> keys in the Python REPL when $TERM is set to vt100.

  • gh-124022: Fix bug where docstring is removed from classes in interactive mode.

  • gh-123958: docstrings are now removed from the optimized AST in optimization level 2.

  • gh-123923: The f_executable field in the internal _PyInterpreterFrame struct now uses a tagged pointer. Profilers and debuggers that uses this field should clear the least significant bit to recover the PyObject* pointer.

  • gh-77894: Fix possible crash in the garbage collector when it tries to break a reference loop containing a memoryview object. Now a memoryview object can only be cleared if there are no buffers that refer it.

  • gh-120221: asyncio REPL is now again properly recognizing KeyboardInterrupts. Display of exceptions raised in secondary threads is fixed.

  • gh-119310: Allow the new interactive shell to read history files written with the editline library that use unicode-escaped entries. Patch by aorcajo and Łukasz Langa.

  • gh-123572: Fix key mappings for various F-keys in Windows for the new REPL. Patch by devdanzin

Library

  • gh-123614: Add turtle.save() to easily save Turtle drawings as PostScript files. Patch by Marie Roald and Yngve Mardal Moe.

Core and Builtins

  • gh-123339: Setting the __module__ attribute for a class now removes the __firstlineno__ item from the type’s dict, so they will no longer be inconsistent.

  • gh-119034: Change <page up> and <page down> keys of the Python REPL to history search forward/backward. Patch by Victor Stinner.

  • gh-123562: Improve SyntaxError message for using case ... as ... with not a name.

  • gh-123545: Fix a double decref in rare cases on experimental JIT builds.

  • gh-123484: Fix _Py_DebugOffsets for long objects to be relative to the start of the object rather than the start of a subobject.

  • gh-123446: Fix empty function name in TypeError when builtin magic methods are used without the required args.

  • gh-123440: Improve SyntaxError message for using except as with not a name.

  • gh-116017: Improved JIT memory consumption by periodically freeing memory used by infrequently-executed code. This change is especially likely to improve the memory footprint of long-running programs.

  • gh-123344: Add AST optimizations for type parameter defaults.

  • gh-123321: Prevent Parser/myreadline race condition from segfaulting on multi-threaded use. Patch by Bar Harel and Amit Wienner.

  • gh-123177: Fix a bug causing stray prompts to appear in the middle of wrapped lines in the new REPL.

  • gh-122982: Extend the deprecation period for bool inversion (~) by two years.

  • gh-123271: Make concurrent iterations over the same zip() iterator safe under free-threading.

  • gh-123275: Support -X gil=1 and PYTHON_GIL=1 on non-free-threaded builds.

  • gh-123177: Deactivate line wrap in the Apple Terminal via a ANSI escape code. Patch by Pablo Galindo

  • gh-123229: Fix valgrind warning by initializing the f-string buffers to 0 in the tokenizer. Patch by Pablo Galindo

  • gh-122298: Restore printout of GC stats when gc.set_debug(gc.DEBUG_STATS) is called. This feature was accidentally removed when implementing incremental GC.

  • gh-121804: Correctly show error locations when a SyntaxError is raised in the basic REPL. Patch by Sergey B Kirpichev.

  • gh-115776: Enables inline values (Python’s equivalent of hidden classes) on any class who’s instances are of a fixed size.

  • gh-123142: Fix too-wide source location in exception tracebacks coming from broken iterables in comprehensions.

  • gh-123048: Fix a bug where pattern matching code could emit a JUMP_FORWARD with no source location.

  • gh-118093: Break up CALL_ALLOC_AND_ENTER_INIT into micro-ops and relax requirement for exact args, in order to increase the amount of code supported by tier 2.

  • gh-123123: Fix displaying SyntaxError exceptions covering multiple lines. Patch by Pablo Galindo

  • gh-123083: Fix a potential use-after-free in STORE_ATTR_WITH_HINT.

  • gh-123022: Fix crash in free-threaded build when calling Py_Initialize() from a non-main thread.

  • gh-118093: Add three specializations for CALL_KW:

    • CALL_KW_PY for calls to Python functions

    • CALL_KW_BOUND_METHOD for calls to bound methods

    • CALL_KW_NON_PY for all other calls

  • gh-122821: Make sure that branches in while statements have consistent offsets for sys.monitoring. while statements are now compiled with a simple jump at the end of the body, instead of duplicating the test.

  • gh-122907: Building with HAVE_DYNAMIC_LOADING now works as well as it did in 3.12. Existing deficiences will be addressed separately. (See https://github.com/python/cpython/issues/122950.)

  • gh-122888: Fix crash on certain calls to str() with positional arguments of the wrong type. Patch by Jelle Zijlstra.

  • gh-118093: Improve the experimental JIT’s handling of polymorphic code.

  • gh-122697: Fixed memory leaks at interpreter shutdown in the free-threaded build, and also reporting of leaked memory blocks via -X showrefcount.

  • gh-116622: Fix Android stdout and stderr messages being truncated or lost.

  • gh-122527: Fix a crash that occurred when a PyStructSequence was deallocated after its type’s dictionary was cleared by the GC. The type’s tp_basicsize now accounts for non-sequence fields that aren’t included in the Py_SIZE of the sequence.

  • gh-122445: Add only fields which are modified via self.* to __static_attributes__.

  • gh-122417: In the free-threaded build, the reference counts for heap type objects are now partially stored in a distributed manner in per-thread arrays. This reduces contention on the heap type’s reference count fields when creating or destroying instances of the same type from multiple threads concurrently.

  • gh-116090: Fix an issue in JIT builds that prevented some for loops from correctly firing RAISE monitoring events.

  • gh-122300: Preserve AST nodes for f-string with single-element format specifiers. Patch by Pablo Galindo

  • gh-120906: frame.f_locals now supports arbitrary hashable objects as keys.

  • gh-122239: When a list, tuple or dict with too many elements is unpacked, show the actual length in the error message.

  • gh-122245: Detection of writes to __debug__ is moved from the compiler’s codegen stage to the symtable. This means that these errors are now detected even in code that is optimized away before codegen (such as assertions with the -O command line option).

  • gh-122234: Specializations for sums with float and complex inputs in sum() now always use compensated summation. Also, for integer items in above specializations: PyLong_AsDouble() is used, instead of PyLong_AsLongAndOverflow(). Patch by Sergey B Kirpichev.

  • gh-122208: Dictionary watchers now only deliver the PyDict_EVENT_ADDED event when the insertion is in a known good state to succeed.

  • gh-122160: Remove the BUILD_CONST_KEY_MAP opcode. Use BUILD_MAP instead.

  • gh-122029: Emit c_call events in sys.setprofile() when a PyMethodObject pointing to a PyCFunction is called.

  • gh-122026: Fix a bug that caused the tokenizer to not correctly identify mismatched parentheses inside f-strings in some situations. Patch by Pablo Galindo

  • gh-99108: Python’s hashlib now unconditionally uses the vendored HACL* library for Blake2. Python no longer accepts libb2 as an optional dependency for Blake2.

    We refreshed HACL* to the latest version, and now vendor HACL*’s 128-bit and 256-bit wide vector implementations for Blake2, which are used on x86/x64 toolchains when the required CPU features are available at runtime.

    HACL*’s 128-bit wide vector implementation of Blake2 can also run on ARM NEON and Power8, but lacking evidence of a performance gain, these are not enabled (yet).

Library

Core and Builtins

  • gh-121860: Fix crash when rematerializing a managed dictionary after it was deleted.

  • gh-121795: Improve performance of set membership testing, set.remove() and set.discard() when the argument is a set.

  • gh-121814: Fixed the SegFault when PyEval_SetTrace() is used with no Python frame on stack.

  • gh-121295: Fix PyREPL console getting into a blocked state after interrupting a long paste

  • gh-121794: Fix bug in free-threaded Python where a resurrected object could lead to a negative ref count assertion failure.

  • gh-121657: Improve the SyntaxError message if the user tries to use yield from outside a function.

  • gh-121609: Fix pasting of characters containing unicode character joiners in the new REPL. Patch by Marta Gomez Macias

  • gh-121297: Previously, incorrect usage of await or asynchronous comprehensions in code removed by the -O option was not flagged by the Python compiler. Now, such code raises SyntaxError. Patch by Jelle Zijlstra.

  • gh-117482: Unexpected slot wrappers are no longer created for builtin static types in subinterpreters.

  • gh-121562: Optimized performance of hex_from_char by replacing switch-case with a lookup table

  • gh-121499: Fix a bug affecting how multi-line history was being rendered in the new REPL after interacting with the new screen cache. Patch by Pablo Galindo

  • gh-121497: Fix a bug that was preventing the REPL to correctly respect the history when an input hook was set. Patch by Pablo Galindo

  • gh-121012: Tier 2 execution now ensures that list iterators remain exhausted, once they become exhausted.

  • gh-121439: Allow tuples of length 20 in the freelist to be reused.

  • gh-121288: ValueError messages for list.index(), range.index(), deque.index(), deque.remove() and ShareableList.index() no longer contain the repr of the searched value (which can be arbitrary large) and are consistent with error messages for other index() and remove() methods.

  • gh-121368: Fix race condition in _PyType_Lookup in the free-threaded build due to a missing memory fence. This could lead to _PyType_Lookup returning incorrect results on arm64.

  • gh-121149: Added specialization for summation of complexes, this also improves accuracy of builtin sum() for such inputs. Patch by Sergey B Kirpichev.

  • gh-121130: Fix f-strings with debug expressions in format specifiers. Patch by Pablo Galindo

Library

  • gh-121381: Remove subprocess._USE_VFORK escape hatch code and documentation. It was added just in case, and doesn’t have any known cases that require it.

Core and Builtins

  • gh-119726: Optimize code layout for calls to C functions from the JIT on AArch64. Patch by Diego Russo.

  • gh-121115: PyLong_AsNativeBytes() no longer uses __index__() methods by default. The Py_ASNATIVEBYTES_ALLOW_INDEX flag has been added to allow it.

  • gh-120838: Py_Finalize() and Py_FinalizeEx() now always run with the main interpreter active.

  • gh-113433: Subinterpreters now get cleaned up automatically during runtime finalization.

  • gh-119726: Improve the speed and memory use of C function calls from JIT code on AArch64. Patch by Diego Russo

  • gh-116017: Simplify the warmup mechanism used for “side exits” in JIT code, resulting in slightly better performance and slightly lower memory usage for most platforms.

  • gh-98442: Fix too wide source locations of the cleanup instructions of a with statement.

  • gh-120754: Reduce the number of system calls invoked when reading a whole file (ex. open('a.txt').read()). For a sample program that reads the contents of the 400+ .rst files in the cpython repository Doc folder, there is an over 10% reduction in system call count.

  • gh-119462: Make sure that invariants of type versioning are maintained: * Superclasses always have their version number assigned before subclasses * The version tag is always zero if the tag is not valid. * The version tag is always non-if the tag is valid.

  • gh-120437: Fix _CHECK_STACK_SPACE optimization problems introduced in gh-118322.

  • gh-120722: Correctly set the bytecode position on return instructions within lambdas. Patch by Jelle Zijlstra.

  • gh-120367: Fix bug where compiler creates a redundant jump during pseudo-op replacement. Can only happen with a synthetic AST that has a try on the same line as the instruction following the exception handler.

  • gh-120507: Remove the BEFORE_WITH and BEFORE_ASYNC_WITH instructions. Add the new LOAD_SPECIAL instruction. Generate code for with and async with statements using the new instruction.

  • gh-113993: Strings interned with sys.intern() are again garbage-collected when no longer used, as per the documentation. Strings interned with the C function PyUnicode_InternInPlace() are still immortal. Internals of the string interning mechanism have been changed. This may affect performance and identities of str objects.

Library

  • gh-120485: Add an override of allow_reuse_port on classes subclassing socketserver.TCPServer where allow_reuse_address is also overridden.

Core and Builtins

  • gh-120384: Fix an array out of bounds crash in list_ass_subscript, which could be invoked via some specifically tailored input: including concurrent modification of a list object, where one thread assigns a slice and another clears it.

  • gh-120367: Fix crash in compiler on code with redundant NOPs and JUMPs which show up after exception handlers are moved to the end of the code.

Library

Core and Builtins

  • gh-120397: Improve the throughput by up to two times for the str.count(), bytes.count() and bytearray.count() methods for counting single characters.

  • gh-120221: Deliver real signals on Ctrl-C and Ctrl-Z in the new REPL. Patch by Pablo Galindo

  • gh-120346: Respect PYTHON_BASIC_REPL when running in interactive inspect mode (python -i). Patch by Pablo Galindo

  • gh-93691: Fix source locations of instructions generated for the iterator of a for statement.

  • gh-120198: Fix a crash when multiple threads read and write to the same __class__ of an object concurrently.

  • gh-120298: Fix use-after free in list_richcompare_impl which can be invoked via some specifically tailored evil input.

  • gh-119666: Fix a compiler crash in the case where two comprehensions in class scope both reference __class__.

  • gh-119726: JIT: Re-use trampolines on AArch64 when creating stencils. Patch by Diego Russo

  • gh-120225: Fix crash in compiler on empty block at end of exception handler.

  • gh-93691: Fix source locations of instructions generated for with statements.

  • gh-120097: FrameLocalsProxy now subclasses collections.abc.Mapping and can be matched as a mapping in match statements

  • gh-120080: Direct call to the int.__round__() now accepts None as a valid argument.

  • gh-119933: Improve SyntaxError messages for invalid expressions in a type parameters bound, a type parameter constraint tuple or a default type parameter. Patch by Bénédikt Tran.

  • gh-119724: Reverted improvements to error messages for elif/else statements not matching any valid statements, which made in hard to locate the syntax errors inside those elif/else blocks.

  • gh-119879: String search is now slightly faster for certain cases. It now utilizes last character gap (good suffix rule) for two-way periodic needles.

  • gh-119842: Honor PyOS_InputHook() in the new REPL. Patch by Pablo Galindo

  • gh-119180: classmethod() and staticmethod() now wrap the __annotations__ and __annotate__ attributes of their underlying callable lazily. See PEP 649. Patch by Jelle Zijlstra.

  • gh-119821: Fix execution of annotation scopes within classes when globals is set to a non-dict. Patch by Jelle Zijlstra.

  • gh-118934: Make PyEval_GetLocals return borrowed reference

  • gh-119740: Remove the previously-deprecated delegation of int() to __trunc__().

  • gh-119689: Generate stack effect metadata for pseudo instructions from bytecodes.c.

  • gh-109218: complex() accepts now a string only as a positional argument. Passing a complex number as the “real” or “imag” argument is deprecated; it should only be passed as a single positional argument.

  • gh-119548: Add a clear command to the REPL. Patch by Pablo Galindo

  • gh-111999: Fix the signature of str.format_map().

  • gh-119560: An invalid assert in beta 1 has been removed. The assert would fail if PyState_FindModule() was used in an extension module’s init function before the module def had been initialized.

  • gh-119369: Fix deadlock during thread deletion in free-threaded build, which could occur when the GIL was enabled at runtime.

  • gh-119525: Fix deadlock involving _PyType_Lookup() cache in the free-threaded build when the GIL is dynamically enabled at runtime.

  • gh-119258: Eliminate type version guards in the tier two interpreter.

    Note that setting the tp_version_tag manually (which has never been supported) may result in crashes.

  • gh-119311: Fix bug where names are unexpectedly mangled in the bases of generic classes.

  • gh-119395: Fix bug where names appearing after a generic class are mangled as if they are in the generic class.

  • gh-119372: Correct invalid corner cases in complex division (resulted in (nan+nanj) output), e.g. 1/complex('(inf+infj)'). Patch by Sergey B Kirpichev.

  • gh-119180: Evaluation of annotations is now deferred. See PEP 649 for details.

  • gh-119180: Replace LOAD_ASSERTION_ERROR opcode with LOAD_COMMON_CONSTANT and add support for NotImplementedError.

  • gh-119213: Non-builtin modules built with argument clinic were crashing if used in a subinterpreter before the main interpreter. The objects that were causing the problem by leaking between interpreters carelessly have been fixed.

  • gh-119011: Fixes type.__type_params__ to return an empty tuple instead of a descriptor.

  • gh-118692: Avoid creating unnecessary StopIteration instances for monitoring.

  • gh-119180: Add an __annotate__ attribute to functions, classes, and modules as part of PEP 649. Patch by Jelle Zijlstra.

  • gh-119049: Fix displaying the source line for warnings created by the C API if the warnings module had not yet been imported.

  • gh-119057: Improve ZeroDivisionError error message. Now, all error messages are harmonized: all /, //, and % operations just use “division by zero” message. And 0 ** -1 operation uses “zero to a negative power”.

  • gh-118844: Fix build failures when configuring with both --disable-gil and --enable-experimental-jit.

  • gh-118921: Add copy() method for FrameLocalsProxy which returns a snapshot dict for local variables.

  • gh-117657: Fix data races on the field that stores a pointer to the interpreter’s main thread that occur in free-threaded builds.

  • gh-118750: If the C version of the decimal module is available, int(str) now uses it to supply an asymptotically much faster conversion. However, this only applies if the string contains over about 2 million digits.

  • gh-118767: Using NotImplemented in a boolean context now raises TypeError. Contributed by Jelle Zijlstra.

  • gh-118561: Fix race condition in free-threaded build where list.extend() could expose uninitialised memory to concurrent readers.

  • gh-117139: Convert the Python evaluation stack to use internal stack references. The purpose is to support tagged pointers. In PEP 703, this will allow for its form of deferred reference counting. For both the default and free-threaded builds, this sets up the infrastructure for unboxed integers in the future.

Library

Core and Builtins

  • gh-117558: Improve error messages when a string, bytes or bytearray object of length 1 is expected.

  • gh-117195: Avoid assertion failure for debug builds when calling object.__sizeof__(1)

  • gh-116022: Improve the __repr__() output of AST nodes.

  • gh-114091: Changed the error message for awaiting something that can’t be awaited from “object <type> can’t be used in an await expression” to “’<type>’ object can’t be awaited”.

  • gh-113190: Py_Finalize() now deletes all interned strings.

  • gh-84978: Add class methods float.from_number() and complex.from_number().

  • gh-95144: Improve the error message from a in b when b is not a container to mention the term “container”.

  • bpo-24766: Fix handling of doc argument to subclasses of property.

C API

Build

  • gh-125269: Fix detection of whether -latomic is needed when cross-compiling CPython using the configure script.

  • gh-123990: Remove WITH_FREELISTS macro and --without-freelists build configuration

  • gh-124102: Update internal documentation under PCbuild, so it now correctly states that Windows requires VS2017 or later and Python 3.10 or later

  • gh-124043: Building using --with-trace-refs is (temporarily) disallowed when the GIL is disabled.

  • gh-123418: Updated Android build to use OpenSSL 3.0.15.

  • gh-123297: Propagate the value of LDFLAGS to LDCXXSHARED in sysconfig. Patch by Pablo Galindo

  • gh-121634: Allow for specifying the target compile triple for WASI.

  • gh-122578: Use WASI SDK 24 for testing.

  • gh-116622: Rename build variable MODULE_LDFLAGS back to LIBPYTHON, as it’s used by package build systems (e.g. Meson).

  • gh-118943: Fix an issue where the experimental JIT could be built several times by the make regen-all target, leading to possible race conditions on heavily parallelized builds.

  • gh-121996: Introduce ./configure –disable-safety and –enable-slower-safety options. Patch by Donghee Na.

  • gh-120522: Added a --with-app-store-compliance option to patch out known issues with macOS/iOS App Store review processes.

  • gh-120371: Support WASI SDK 22 by explicitly skipping functions that are just stubs in wasi-libc.

  • gh-121731: Fix mimalloc compile error on GNU/Hurd

  • gh-121487: Fix deprecation warning for ATOMIC_VAR_INIT in mimalloc.

  • gh-121467: Fix a Makefile bug that prevented mimalloc header files from being installed.

  • gh-121103: On POSIX systems, excluding macOS framework installs, the lib directory for the free-threaded build now includes a “t” suffix to avoid conflicts with a co-located default build installation.

  • gh-120831: The default minimum iOS version was increased to 13.0.

  • gh-121082: Fix build failure when the developer use --enable-pystats arguments in configuration command after #118450.

  • gh-120671: Fix failing configure tests due to a missing space when appending to CFLAGS.

  • gh-120602: Correctly handle LLVM installs with LLVM_VERSION_SUFFIX when building with --enable-experimental-jit.

  • gh-120688: On WASI in debug mode, Python is now built with compiler flag -O3 instead of -Og, to support more recursive calls. Patch by Victor Stinner.

  • gh-118943: Fix a possible race condition affecting parallel builds configured with --enable-experimental-jit, in which FileNotFoundError could be caused by another process already moving jit_stencils.h.new to jit_stencils.h.

  • gh-120326: On Windows, fix build error when --disable-gil and --experimental-jit options are combined.

  • gh-120291: Make the python-config shell script compatible with non-bash shells.

  • gh-113565: Improve curses and curses.panel dependency checks in configure.

  • gh-119729: On POSIX systems, the pkg-config (.pc) filenames now include the ABI flags, which may include debug (“d”) and free-threaded (“t”). For example: * python-3.14.pc (default, non-debug build) * python-3.14d.pc (default, debug build) * python-3.14t.pc (free-threaded build)

  • gh-119400: make_ssl_certs, the script that prepares certificate data for the test suite, now allows specifying expiration dates.

  • gh-115119: Fall back to the bundled libmpdec if a system version cannot be found.

  • gh-119132: Update sys.version to identify whether the build is default build or free-threading build. Patch By Donghee Na.

  • gh-118836: Fix an AssertionError when building with --enable-experimental-jit and the compiler emits a SHT_NOTE section.

  • gh-118943: Fix a possible race condition affecting parallel builds configured with --enable-experimental-jit, in which compilation errors could be caused by an incompletely-generated header file.

Python 3.13.0 beta 1

Release date: 2024-05-08

Security

  • gh-116741: Update bundled libexpat to 2.6.2

  • gh-117233: Detect BLAKE2, SHA3, Shake, & truncated SHA512 support in the OpenSSL-ish libcrypto library at build time. This allows hashlib to be used with libraries that do not to support every algorithm that upstream OpenSSL does.

Core and Builtins

  • gh-118414: Add instrumented opcodes to YIELD_VALUE assertion for tracing cases.

  • gh-117953: When a builtin or extension module is imported for the first time, while a subinterpreter is active, the module’s init function is now run by the main interpreter first before import continues in the subinterpreter. Consequently, single-phase init modules now fail in an isolated subinterpreter without the init function running under that interpreter, whereas before it would run under the subinterpreter before failing, potentially leaving behind global state and callbacks and otherwise leaving the module in an inconsistent state.

  • gh-117549: Don’t use designated initializer syntax in inline functions in internal headers. They cause problems for C++ or MSVC users who aren’t yet using the latest C++ standard (C++20). While internal, pycore_backoff.h, is included (indirectly, via pycore_code.h) by some key 3rd party software that does so for speed.

Library

  • gh-95382: Improve performance of json.dumps() and json.dump() when using the argument indent. Depending on the data the encoding using json.dumps() with indent can be up to 2 to 3 times faster.

Core and Builtins

  • gh-116322: In --disable-gil builds, the GIL will be enabled while loading C extension modules. If the module indicates that it supports running without the GIL, the GIL will be disabled once loading is complete. Otherwise, the GIL will remain enabled for the remainder of the interpreter’s lifetime. This behavior does not apply if the GIL has been explicitly enabled or disabled with PYTHON_GIL or -Xgil.

  • gh-118513: Fix incorrect UnboundLocalError when two comprehensions in the same function both reference the same name, and in one comprehension the name is bound while in the other it’s an implicit global.

  • gh-118518: Allow the Linux perf support to work without frame pointers using perf’s advanced JIT support. The feature is activated when using the PYTHON_PERF_JIT_SUPPORT environment variable or when running Python with -Xperf_jit. Patch by Pablo Galindo.

  • gh-117514: Add sys._is_gil_enabled() function that returns whether the GIL is currently enabled. In the default build it always returns True because the GIL is always enabled. In the free-threaded build, it may return True or False.

  • gh-118164: Break a loop between the Python implementation of the decimal module and the Python code for integer to string conversion. Also optimize integer to string conversion for values in the range from 9_000 to 135_000 decimal digits.

  • gh-118473: Fix sys.set_asyncgen_hooks() not to be partially set when raising TypeError.

  • gh-118465: Compiler populates the new __firstlineno__ field on a class with the line number of the first line of the class definition.

  • gh-118492: Fix an issue where the type cache can expose a previously accessed attribute when a finalizer is run.

  • gh-117714: update async_generator.athrow().close() and async_generator.asend().close() to close their section of the underlying async generator

  • gh-111201: The interactive interpreter is now implemented in Python, which allows for a number of new features like colors, multiline input, history viewing, and paste mode. Contributed by Pablo Galindo, Łukasz Langa and Lysandros Nikolaou based on code from the PyPy project.

  • gh-74929: Implement PEP 667: converted FrameType.f_locals and PyFrame_GetLocals() to return a write-through proxy object when the frame refers to a function or comprehension.

  • gh-116767: Fix crash in compiler on ‘async with’ that has many context managers.

  • gh-118335: Change how to use the tier 2 interpreter. Instead of running Python with -X uops or setting the environment variable PYTHON_UOPS=1, this choice is now made at build time by configuring with --enable-experimental-jit=interpreter.

    Beware! This changes the environment variable to enable or disable micro-ops to PYTHON_JIT. The old PYTHON_UOPS is no longer used.

  • gh-118306: Update JIT compilation to use LLVM 18

  • gh-118160: Annotation scopes within classes can now contain comprehensions. However, such comprehensions are not inlined into their parent scope at runtime. Patch by Jelle Zijlstra.

  • gh-118272: Fix bug where generator.close does not free the generator frame’s locals.

  • gh-118216: Don’t consider __future__ imports with dots before the module name.

  • gh-118074: Make sure that the Executor objects in the COLD_EXITS array aren’t assumed to be GC-able (which would access bytes outside the object).

  • gh-107674: Lazy load frame line number to improve performance of tracing

  • gh-118082: Improve SyntaxError message for imports without names, like in from x import and import cases. It now points out to users that import expects at least one name after it.

  • gh-118090: Improve SyntaxError message for empty type param brackets.

  • gh-117958: Added a get_jit_code() method to access JIT compiled machine code from the UOp Executor when the experimental JIT is enabled. Patch by Anthony Shaw.

  • gh-117901: Add option for compiler’s codegen to save nested instruction sequences for introspection.

  • gh-116622: Redirect stdout and stderr to system log when embedded in an Android app.

  • gh-109118: annotation scope within class scopes can now contain lambdas.

  • gh-117894: Prevent agen.aclose() objects being re-used after .throw().

  • gh-117881: prevent concurrent access to an async generator via athrow().throw() or asend().throw()

  • gh-117536: Fix a RuntimeWarning when calling agen.aclose().throw(Exception).

  • gh-117755: Fix mimalloc allocator for huge memory allocation (around 8,589,934,592 GiB) on s390x. Patch by Victor Stinner.

  • gh-117750: Fix issue where an object’s dict would get out of sync with the object’s internal values when being cleared. obj.__dict__.clear() now clears the internal values, but leaves the dict attached to the object.

  • gh-117431: Improve the performance of the following bytes and bytearray methods by adapting them to the METH_FASTCALL calling convention:

    • count()

    • find()

    • index()

    • rfind()

    • rindex()

  • gh-117709: Speed up calls to str() with positional-only argument, by using the PEP 590 vectorcall calling convention. Patch by Erlend Aasland.

  • gh-117680: Give _PyInstructionSequence a Python interface and use it in tests.

  • gh-115776: Statically allocated objects are, by definition, immortal so must be marked as such regardless of whether they are in extension modules or not.

  • gh-117385: Remove unhandled PY_MONITORING_EVENT_BRANCH and PY_MONITORING_EVENT_EXCEPTION_HANDLED events from sys.settrace().

  • gh-116322: Extension modules may indicate to the runtime that they can run without the GIL. Multi-phase init modules do so by calling providing Py_MOD_GIL_NOT_USED for the Py_mod_gil slot, while single-phase init modules call PyUnstable_Module_SetGIL(mod, Py_MOD_GIL_NOT_USED) from their init function.

  • gh-116129: Implement PEP 696, adding support for defaults on type parameters. Patch by Jelle Zijlstra.

  • gh-93502: Add two new functions to the C-API, PyRefTracer_SetTracer() and PyRefTracer_GetTracer(), that allows to track object creation and destruction the same way the tracemalloc module does. Patch by Pablo Galindo

  • gh-107674: Improved the performance of sys.settrace() significantly

  • gh-95754: Improve the error message when a script shadowing a module from the standard library causes AttributeError to be raised. Similarly, improve the error message when a script shadowing a third party module attempts to access an attribute from that third party module while still initialising.

  • gh-99180: Elide uninformative traceback indicators in return and simple assignment statements. Patch by Pablo Galindo.

  • gh-105879: Allow the globals and locals arguments to exec() and eval() to be passed as keywords.

Library

  • gh-118418: A DeprecationWarning is now emitted if you fail to pass a value to the new type_params parameter of typing._eval_type() or typing.ForwardRef._evaluate(). (Using either of these private and undocumented functions is discouraged to begin with, but failing to pass a value to the type_params parameter may lead to incorrect behaviour on Python 3.12 or newer.)

  • gh-118660: Add an optional second type parameter to typing.ContextManager and typing.AsyncContextManager, representing the return types of __exit__() and __aexit__() respectively. This parameter defaults to bool | None.

  • gh-118650: The enum module allows method named _repr_* to be defined on Enum types.

  • gh-118648: Add type parameter defaults to typing.Generator and typing.AsyncGenerator.

  • gh-101137: Mime type text/x-rst is now supported by mimetypes.

  • gh-118164: The Python implementation of the decimal module could appear to hang in relatively small power cases (like 2**117) if context precision was set to a very high value. A different method to check for exactly representable results is used now that doesn’t rely on computing 10**precision (which could be effectively too large to compute).

  • gh-111744: breakpoint() and pdb.set_trace() now enter the debugger immediately after the call rather than before the next line is executed.

  • gh-118500: Add pdb support for zipapps

  • gh-118406: Add signature for sqlite3.Connection objects.

  • gh-101732: Use a Y2038 compatible openssl time function when available.

  • gh-118404: Fix inspect.signature() for non-comparable callables.

  • gh-118402: Fix inspect.signature() for the result of the functools.cmp_to_key() call.

  • gh-116622: On Android, sysconfig.get_platform now returns the format specified by PEP 738.

  • gh-118285: Allow to specify the signature of custom callable instances of extension type by the __text_signature__ attribute. Specify signatures of operator.attrgetter, operator.itemgetter, and operator.methodcaller instances.

  • gh-118314: Fix an edge case in binascii.a2b_base64() strict mode, where excessive padding is not detected when no padding is necessary.

  • gh-118271: Add the PhotoImage methods read() to read an image from a file and data() to get the image data. Add background and grayscale parameters to PhotoImage method write().

  • gh-118225: Add the PhotoImage method copy_replace() to copy a region from one image to other image, possibly with pixel zooming and/or subsampling. Add from_coords parameter to PhotoImage methods copy(), zoom() and subsample(). Add zoom and subsample parameters to PhotoImage method copy().

  • gh-118221: Fix a bug where sqlite3.Connection.iterdump() could fail if a custom row factory was used. Patch by Erlend Aasland.

  • gh-118013: Fix regression introduced in gh-103193 that meant that calling inspect.getattr_static() on an instance would cause a strong reference to that instance’s class to persist in an internal cache in the inspect module. This caused unexpected memory consumption if the class was dynamically created, the class held strong references to other objects which took up a significant amount of memory, and the cache contained the sole strong reference to the class. The fix for the regression leads to a slowdown in getattr_static(), but the function should still be significantly faster than it was in Python 3.11. Patch by Alex Waygood.

  • gh-118218: Speed up itertools.pairwise() in the common case by up to 1.8x.

  • gh-117486: Improve the behavior of user-defined subclasses of ast.AST. Such classes will now require no changes in the usual case to conform with the behavior changes of the ast module in Python 3.13. Patch by Jelle Zijlstra.

  • gh-90848: Fixed unittest.mock.create_autospec() to configure parent mock with keyword arguments.

  • gh-118168: Fix incorrect argument substitution when typing.Unpack is used with the builtin tuple. typing.Unpack now raises TypeError when used with certain invalid types. Patch by Jelle Zijlstra.

  • gh-118131: Add command-line interface for the random module. Patch by Hugo van Kemenade.

  • gh-118107: Fix zipimport reading of ZIP64 files with file entries that are too big or offset too far.

  • gh-102511: Fix os.path.normpath() for UNC paths on Windows. Speed up os.path.splitroot() with a native implementation.

  • gh-117535: Change the unknown filename of warnings from sys to <sys> to clarify that it’s not a real filename.

  • gh-114053: Fix erroneous NameError when calling typing.get_type_hints() on a class that made use of PEP 695 type parameters in a module that had from __future__ import annotations at the top of the file. Patch by Alex Waygood.

  • gh-116931: Add parameter fileobj check for tarfile.TarFile.addfile()

  • gh-117995: Don’t raise DeprecationWarning when a sequence of parameters is used to bind indexed, nameless placeholders. See also gh-100668.

  • gh-80361: Fix TypeError in email.message.Message.get_payload() when the charset is RFC 2231 encoded.

  • gh-86650: Fix IndexError when parse some emails with invalid Message-ID (including one-off addresses generated by Microsoft Outlook).

  • gh-117691: Improve the error messages emitted by tarfile deprecation warnings relating to PEP 706. If a filter argument is not provided to extract() or extractall, the deprecation warning now points to the line in the user’s code where the relevant function was called. Patch by Alex Waygood.

  • gh-115874: Fixed a possible segfault during garbage collection of _asyncio.FutureIter objects. Patch by Savannah Ostrowski.

  • gh-115060: Speed up pathlib.Path.glob() by omitting an initial is_dir() call. As a result of this change, glob() can no longer raise OSError.

  • gh-77102: site module now parses .pth file with UTF-8 first, and locale encoding if UnicodeDecodeError happened. It supported only locale encoding before.

  • gh-76785: We’ve exposed the low-level _interpreters module for the sake of the PyPI implementation of PEP 734. It was sometimes available as the _xxsubinterpreters module and was formerly used only for testing. For the most part, it should be considered an internal module, like _thread and _imp. See https://discuss.python.org/t/pep-734-multiple-interpreters-in-the-stdlib/41147/26.

  • gh-115060: Speed up pathlib.Path.glob() by not scanning directories for non-wildcard pattern segments.

  • gh-117727: Speed up pathlib.Path.iterdir() by using os.scandir() internally.

  • gh-117586: Speed up pathlib.Path.walk() by working with strings internally.

  • gh-117722: Change the new multi-separator support in asyncio.StreamReader.readuntil() to only accept tuples of separators rather than arbitrary iterables.

  • gh-117692: Fixes a bug when doctest.DocTestFinder was failing on wrapped builtin_function_or_method.

  • gh-117348: Largely restored import time performance of configparser by avoiding dataclasses.

  • gh-117641: Speedup os.path.commonpath() on Unix.

  • gh-117663: Fix _simple_enum to detect aliases when multiple arguments are present but only one is the member value.

  • gh-117636: Speedup os.path.join().

  • gh-117618: Support package.module as filename for break command of pdb

  • gh-102247: the status codes enum with constants in http.HTTPStatus are updated to include the names from RFC9110. This RFC includes some HTTP statuses previously only used for WEBDAV and assigns more generic names to them.

    The old constants are preserved for backwards compatibility.

  • gh-117607: Speedup os.path.relpath().

  • gh-117586: Speed up pathlib.Path.glob() by working with strings internally.

  • gh-117225: Add colour to doctest output. Patch by Hugo van Kemenade.

  • gh-117566: ipaddress.IPv6Address.is_loopback() will now return True for IPv4-mapped loopback addresses, i.e. addresses in the ::ffff:127.0.0.0/104 address space.

  • gh-117546: Fix issue where os.path.realpath() stopped resolving symlinks after encountering a symlink loop on POSIX.

  • gh-116720: Improved behavior of asyncio.TaskGroup when an external cancellation collides with an internal cancellation. For example, when two task groups are nested and both experience an exception in a child task simultaneously, it was possible that the outer task group would misbehave, because its internal cancellation was swallowed by the inner task group.

    In the case where a task group is cancelled externally and also must raise an ExceptionGroup, it will now call the parent task’s cancel() method. This ensures that a asyncio.CancelledError will be raised at the next await, so the cancellation is not lost.

    An added benefit of these changes is that task groups now preserve the cancellation count (asyncio.Task.cancelling()).

    In order to handle some corner cases, asyncio.Task.uncancel() may now reset the undocumented _must_cancel flag when the cancellation count reaches zero.

  • gh-117516: Add typing.TypeIs, implementing PEP 742. Patch by Jelle Zijlstra.

  • gh-117503: Fix support of non-ASCII user names in bytes paths in os.path.expanduser() on Posix.

  • gh-117394: os.path.ismount() is now 2-3 times faster if the user has permissions.

  • gh-117313: Only treat '\n', '\r' and '\r\n' as line separators in re-folding the email messages. Preserve control characters '\v', '\f', '\x1c', '\x1d' and '\x1e' and Unicode line separators '\x85', '\u2028' and '\u2029' as is.

  • gh-117142: Convert _ctypes to multi-phase initialisation (PEP 489).

  • gh-66543: Add the mimetypes.guess_file_type() function which works with file path. Passing file path instead of URL in guess_type() is soft deprecated.

  • gh-68583: webbrowser CLI: replace getopt with argparse, add long options. Patch by Hugo van Kemenade.

  • gh-116871: Name suggestions for AttributeError and ImportError now only include underscored names if the original name was underscored.

  • gh-116023: Don’t show empty fields (value None or []) in ast.dump() by default. Add show_empty=False parameter to optionally show them.

  • gh-115961: Added name and mode attributes for compressed and archived file-like objects in modules bz2, lzma, tarfile and zipfile. The value of the mode attribute of gzip.GzipFile was changed from integer (1 or 2) to string ('rb' or 'wb'). The value of the mode attribute of the readable file-like object returned by zipfile.ZipFile.open() was changed from 'r' to 'rb'.

  • gh-82062: Fix inspect.signature() to correctly handle parameter defaults on methods in extension modules that use names defined in the module namespace.

  • gh-83856: Honor atexit for all multiprocessing start methods

  • gh-113081: Print colorized exception just like built-in traceback in pdb

  • gh-112855: Speed up pickling of pathlib.PurePath objects. Patch by Barney Gale.

  • gh-111744: Support opcode events in bdb

  • gh-109617: ncurses: fixed a crash that could occur on macOS 13 or earlier when Python was built with Apple Xcode 15’s SDK.

  • gh-83151: Enabled arbitrary statements and evaluations in pdb shell to access the local variables of the current frame, which made it possible for multi-scope code like generators or nested function to work.

  • gh-110209: Add __class_getitem__() to types.GeneratorType and types.CoroutineType for type hinting purposes. Patch by James Hilton-Balfe.

  • gh-108191: The types.SimpleNamespace now accepts an optional positional argument which specifies initial values of attributes as a dict or an iterable of key-value pairs.

  • gh-62090: Fix assertion errors caused by whitespace in metavars or SUPPRESS-ed groups in argparse by simplifying usage formatting. Patch by Ali Hamdan.

  • gh-102402: Adjust logging.LogRecord to use time.time_ns() and fix minor bug related to floating-point math.

  • gh-100242: Bring pure Python implementation functools.partial.__new__ more in line with the C-implementation by not just always checking for the presence of the attribute 'func' on the first argument of partial. Instead, both the Python version and the C version perform an isinstance(func, partial) check on the first argument of partial.

  • gh-99730: HEAD requests are no longer upgraded to GET request during redirects in urllib.

  • gh-66410: Setting the tkinter module global wantobjects to 2 before creating the Tk object or call the wantobjects() method of the Tk object with argument 2 makes now arguments to callbacks registered in the tkinter module to be passed as various Python objects (int, float, bytes, tuple), depending on their internal representation in Tcl, instead of always str. tkinter.wantobjects is now set to 2 by default.

  • bpo-40943: Fix several IndexError when parse emails with truncated Message-ID, address, routes, etc, e.g. example@.

  • bpo-39324: Add mime type mapping for .md <-> text/markdown

  • bpo-18108: shutil.chown() now supports dir_fd and follow_symlinks keyword arguments.

  • bpo-30988: Fix parsing of emails with invalid address headers having a leading or trailing dot. Patch by tsufeki.

  • bpo-32839: Add the after_info() method for Tkinter widgets.

Documentation

  • gh-117928: The minimum Sphinx version required for the documentation is now 6.2.1.

Build

  • gh-118734: Fixes Windows build when invoked directly (not through the build.bat script) without specifying a value for UseTIER2.

  • gh-115119: The configure option --with-system-libmpdec now defaults to yes. The bundled copy of libmpdecimal will be removed in Python 3.15.

  • gh-117845: Fix building against recent libedit versions by detecting readline hook signatures in configure.

  • gh-116622: A testbed project was added to run the test suite on Android.

  • gh-117645: Increase WASI stack size from 512 KiB to 8 MiB and the initial memory from 10 MiB to 20 MiB. Patch by Victor Stinner.

  • gh-115119: configure now uses pkg-config to detect decimal dependencies if the --with-system-libmpdec option is given.

Windows

  • gh-115119: Update Windows installer to use libmpdecimal 4.0.0.

  • gh-118486: os.mkdir() now accepts mode of 0o700 to restrict the new directory to the current user.

  • gh-118347: Fixes launcher updates not being installed.

  • gh-118293: The multiprocessing module now passes the STARTF_FORCEOFFFEEDBACK flag when spawning processes to tell Windows not to change the mouse cursor.

  • gh-115009: Update Windows installer to use SQLite 3.45.3.

  • gh-90329: Suppress the warning displayed on virtual environment creation when the requested and created paths differ only by a short (8.3 style) name. Warnings will continue to be shown if a junction or symlink in the path caused the venv to be created in a different location than originally requested.

  • gh-117786: Fixes virtual environments not correctly launching when created from a Store install.

macOS

  • gh-115119: Update macOS installer to use libmpdecimal 4.0.0.

  • gh-114099: iOS preprocessor symbol usage was made compatible with older macOS SDKs.

  • gh-115009: Update macOS installer to use SQLite 3.45.3.

  • gh-91629: Use ~/.config/fish/conf.d configs and fish_add_path to set PATH when installing for the Fish shell.

IDLE

  • bpo-34774: Use user-selected color theme for Help => IDLE Doc.

C API

Python 3.13.0 alpha 6

Release date: 2024-04-09

Core and Builtins

  • gh-117494: Refactored the instruction sequence data structure out of compile.c into instruction_sequence.c.

  • gh-116968: Introduce a unified 16-bit backoff counter type (_Py_BackoffCounter), shared between the Tier 1 adaptive specializer and the Tier 2 optimizer. The API used for adaptive specialization counters is changed but the behavior is (supposed to be) identical.

    The behavior of the Tier 2 counters is changed:

    • There are no longer dynamic thresholds (we never varied these).

    • All counters now use the same exponential backoff.

    • The counter for JUMP_BACKWARD starts counting down from 16.

    • The temperature in side exits starts counting down from 64.

  • gh-117431: Improve the performance of the following bytes and bytearray methods by adapting them to the METH_FASTCALL calling convention:

    • endswith()

    • startswith()

  • gh-117431: Improve the performance of the following str methods by adapting them to the METH_FASTCALL calling convention:

  • gh-117411: Move PyFutureFeatures to an internal header and make it private.

  • gh-109120: Added handle of incorrect star expressions, e.g f(3, *). Patch by Grigoryev Semyon

  • gh-117266: Fix crashes for certain user-created subclasses of ast.AST. Such classes are now expected to set the _field_types attribute.

  • gh-99108: Updated the hashlib built-in HACL* project C code from upstream that we use for many implementations when they are not present via OpenSSL in a given build. This also avoids the rare potential for a C symbol name one definition rule linking issue.

  • gh-117108: Change the old space bit of objects in the young generation from 0 to gcstate->visited, so that any objects created during GC will have the old bit set correctly if they get moved into the old generation.

  • gh-117108: The cycle GC now chooses the size of increments based on the total heap size, instead of the rate of object creation. This ensures that it can keep up with growing heaps.

  • gh-116735: For INSTRUMENTED_CALL_FUNCTION_EX, set arg0 to sys.monitoring.MISSING instead of None for CALL event.

  • gh-113964: Starting new threads and process creation through os.fork() are now only prevented once all non-daemon threads exit.

  • gh-116626: Ensure INSTRUMENTED_CALL_FUNCTION_EX always emits CALL

  • gh-116554: list.sort() now exploits more cases of partial ordering, particularly those with long descending runs with sub-runs of equal values. Those are recognized as single runs now (previously, each block of repeated values caused a new run to be created).

  • gh-114099: Added a Loader that can discover extension modules in an iOS-style Frameworks folder.

  • gh-115775: Compiler populates the new __static_attributes__ field on a class with the names of attributes of this class which are accessed through self.X from any function in its body.

  • gh-115776: The array of values, the PyDictValues struct is now embedded in the object during allocation. This provides better performance in the common case, and does not degrade as much when the object’s __dict__ is materialized.

  • gh-108362: Implement an incremental cyclic garbage collector. By collecting the old generation in increments, there is no need for a full heap scan. This can hugely reduce maximum pause time for programs with large heaps.

    Reduce the number of generations from three to two. The old generation is split into two spaces, “visited” and “pending”.

    Collection happens in two steps:: * An increment is formed from the young generation and a small part of the pending space. * This increment is scanned and the survivors moved to the end of the visited space.

    When the collecting space becomes empty, the two spaces are swapped.

Library

  • gh-109870: Dataclasses now calls exec() once per dataclass, instead of once per method being added. This can speed up dataclass creation by up to 20%.

  • gh-97901: Mime type text/rtf is now supported by mimetypes.

Core and Builtins

  • bpo-24612: Improve the SyntaxError that happens when ‘not’ appears after an operator. Patch by Pablo Galindo

Library

  • gh-117648: Improve performance of os.path.join() and os.path.expanduser().

  • gh-117584: Raise TypeError for non-paths in posixpath.relpath.

  • gh-117467: Preserve mailbox ownership when rewriting in mailbox.mbox.flush. Patch by Tony Mountifield.

  • gh-114848: Raise FileNotFoundError when getcwd() returns ‘(unreachable)’, which can happen on Linux >= 2.6.36 with glibc < 2.27.

  • gh-117459: asyncio.asyncio.run_coroutine_threadsafe() now keeps the traceback of CancelledError, TimeoutError and InvalidStateError which are raised in the coroutine.

  • gh-117381: Fix error message for ntpath.commonpath().

  • gh-117337: Deprecate undocumented glob.glob0() and glob.glob1() functions. Use glob.glob() and pass a directory to its root_dir argument instead.

  • gh-117349: Optimise several functions in os.path.

  • gh-117348: Refactored configparser.RawConfigParser._read() to reduce cyclometric complexity and improve comprehensibility.

  • gh-117335: Raise TypeError for non-sequences for ntpath.commonpath().

  • gh-66449: configparser.ConfigParser now accepts unnamed sections before named ones, if configured to do so.

  • gh-88014: In documentation of gzip.GzipFile in module gzip, explain data type of optional constructor argument mtime, and recommend mtime = 0 for generating deterministic streams.

  • gh-117310: Fixed an unlikely early & extra Py_DECREF triggered crash in ssl when creating a new _ssl._SSLContext if CPython was built implausibly such that the default cipher list is empty or the SSL library it was linked against reports a failure from its C SSL_CTX_set_cipher_list() API.

  • gh-117294: A DocTestCase now reports as skipped if all examples in the doctest are skipped.

  • gh-98966: In subprocess, raise a more informative message when stdout=STDOUT.

  • gh-117225: doctest: only print “and X failed” when non-zero, don’t pluralise “1 items”. Patch by Hugo van Kemenade.

  • gh-117205: Speed up compileall.compile_dir() by 20% when using multiprocessing by increasing chunksize.

  • gh-117178: Fix regression in lazy loading of self-referential modules, introduced in gh-114781.

  • gh-112383: Fix dis module’s handling of ENTER_EXECUTOR instructions.

  • gh-117182: Lazy-loading of modules that modify their own __class__ no longer reverts the __class__ to types.ModuleType.

  • gh-117084: Fix zipfile extraction for directory entries with the name containing backslashes on Windows.

  • gh-117114: Make os.path.isdevdrive() available on all platforms. For those that do not offer Dev Drives, it will always return False.

  • gh-117110: Fix a bug that prevents subclasses of typing.Any to be instantiated with arguments. Patch by Chris Fu.

  • gh-109653: Deferred select imports in importlib.metadata and importlib.resources for a 14% speedup.

  • gh-70647: Start the deprecation period for the current behavior of datetime.datetime.strptime() and time.strptime() which always fails to parse a date string with a ValueError involving a day of month such as strptime("02-29", "%m-%d") when a year is not specified and the date happen to be February 29th. This should help avoid users finding new bugs every four years due to a natural mistaken assumption about the API when parsing partial date values.

  • gh-116987: Fixed inspect.findsource() for class code objects.

  • gh-114099: Modify standard library to allow for iOS platform differences.

  • gh-90872: On Windows, subprocess.Popen.wait() no longer calls WaitForSingleObject() with a negative timeout: pass 0 ms if the timeout is negative. Patch by Victor Stinner.

  • gh-116957: configparser: Don’t leave ConfigParser values in an invalid state (stored as a list instead of a str) after an earlier read raised DuplicateSectionError or DuplicateOptionError.

  • gh-115538: _io.WindowsConsoleIO now emit a warning if a boolean value is passed as a filedescriptor argument.

  • gh-90095: Ignore empty lines and comments in .pdbrc

  • gh-106531: Refreshed zipfile._path from zipp 3.18, providing better compatibility for PyPy, better glob performance for deeply nested zipfiles, and providing internal access to CompleteDirs.inject for use in other tests (like importlib.resources).

  • gh-63207: On Windows, time.time() now uses the GetSystemTimePreciseAsFileTime() clock to have a resolution better than 1 us, instead of the GetSystemTimeAsFileTime() clock which has a resolution of 15.6 ms. Patch by Victor Stinner.

  • gh-116764: Restore support of None and other false values in urllib.parse functions parse_qs() and parse_qsl(). Also, they now raise a TypeError for non-zero integers and non-empty sequences.

  • gh-116811: In PathFinder.invalidate_caches, delegate to MetadataPathFinder.invalidate_caches.

  • gh-116647: Fix recursive child in dataclasses

  • gh-113171: Fixed various false positives and false negatives in

    Also in the corresponding ipaddress.IPv4Network and ipaddress.IPv6Network attributes.

  • gh-63283: In encodings.idna, any capitalization of the ACE prefix (xn--) is now acceptable. Patch by Pepijn de Vos and Zackery Spytz.

  • gh-71042: Add platform.android_ver(), which provides device and OS information on Android.

  • gh-73468: Added new math.fma() function, wrapping C99’s fma() operation: fused multiply-add function. Patch by Mark Dickinson and Victor Stinner.

  • gh-116608: The importlib.resources functions is_resource(), open_binary(), open_text(), path(), read_binary(), and read_text() are un-deprecated, and support subdirectories via multiple positional arguments. The contents() function also allows subdirectories, but remains deprecated.

  • gh-116484: Change automatically generated tkinter.Checkbutton widget names to avoid collisions with automatically generated tkinter.ttk.Checkbutton widget names within the same parent widget.

  • gh-114314: In ctypes, ctype data is now stored in type objects directly rather than in a dict subclass. This is an internal change that should not affect usage.

  • gh-116401: Fix blocking os.fwalk() and shutil.rmtree() on opening named pipe.

  • gh-71052: Implement ctypes.util.find_library() on Android.

  • gh-90535: Fix support of interval values > 1 in logging.TimedRotatingFileHandler for when='MIDNIGHT' and when='Wx'.

  • gh-113308: Remove some internal protected parts from uuid: _has_uuid_generate_time_safe, _netbios_getnode, _ipconfig_getnode, and _load_system_functions. They were unused.

  • gh-115627: Fix the ssl module error handling of connection terminate by peer. It now throws an OSError with the appropriate error code instead of an EOFError.

  • gh-114847: Speed up os.path.realpath() on non-Windows platforms.

  • gh-114271: Fix a race in threading.Thread.join().

    threading._MainThread now always represents the main thread of the main interpreter.

    PyThreadState.on_delete and PyThreadState.on_delete_data have been removed.

  • gh-113538: Add asyncio.Server.close_clients() and asyncio.Server.abort_clients() methods which allow to more forcefully close an asyncio server.

  • gh-85287: Changes Unicode codecs to return UnicodeEncodeError or UnicodeDecodeError, rather than just UnicodeError.

  • gh-113548: pdb now allows CLI arguments to pdb -m.

  • gh-112948: Make completion of pdb similar to Python REPL

  • gh-105866: Fixed _get_slots bug which caused error when defining dataclasses with slots and a weakref_slot.

  • gh-96471: Add asyncio.Queue termination with shutdown() method.

  • gh-89739: The zipimport module can now read ZIP64 files.

  • bpo-33533: asyncio.as_completed() now returns an object that is both an asynchronous iterator and plain iterator. The new asynchronous iteration pattern allows for easier correlation between prior tasks and their completed results. This is a closer match to concurrent.futures.as_completed()’s iteration pattern. Patch by Justin Arthur.

  • bpo-27578: inspect.getsource() (and related functions) work with empty module files, returning '\n' (or reasonable equivalent) instead of raising OSError. Patch by Kernc.

  • bpo-37141: Accept an iterable of separators in asyncio.StreamReader.readuntil(), stopping when one of them is encountered.

  • gh-66543: Make mimetypes.guess_type() properly parsing of URLs with only a host name, URLs containing fragment or query, and filenames with only a UNC sharepoint on Windows. Based on patch by Dong-hee Na.

  • bpo-15010: unittest.TestLoader.discover() now saves the original value of unittest.TestLoader._top_level_dir and restores it at the end of the call.

Documentation

  • gh-115977: Remove compatibility references to Emscripten.

  • gh-114099: Add an iOS platform guide, and flag modules not available on iOS.

  • gh-91565: Changes to documentation files and config outputs to reflect the new location for reporting bugs - i.e. GitHub rather than bugs.python.org.

Tests

  • gh-83434: Disable JUnit XML output (--junit-xml=FILE command line option) in regrtest when hunting for reference leaks (-R option). Patch by Victor Stinner.

  • gh-117187: Fix XML tests for vanilla Expat <2.6.0.

  • gh-116333: Tests of TLS related things (error codes, etc) were updated to be more lenient about specific error message strings and behaviors as seen in the BoringSSL and AWS-LC forks of OpenSSL.

  • gh-117089: Consolidated tests for importlib.metadata in their own metadata package.

  • gh-115979: Update test_importlib so that it passes under WASI SDK 21.

  • gh-112536: Add –tsan to test.regrtest for running TSAN tests in reasonable execution times. Patch by Donghee Na.

  • gh-116307: Added import helper isolated_modules as CleanImport does not remove modules imported during the context. Use it in importlib.resources tests to avoid leaving mod around to impede importlib.metadata tests.

Build

  • gh-114736: Have WASI builds use WASI SDK 21.

  • gh-115983: Skip building test modules that must be built as shared under WASI.

  • gh-71052: Add Android build script and instructions.

Windows

  • gh-117267: Ensure DirEntry.stat().st_ctime behaves consistently with os.stat() during the deprecation period of st_ctime by containing the same value as st_birthtime. After the deprecation period, st_ctime will be the metadata change time (or unavailable through DirEntry), and only st_birthtime will contain the creation time.

  • gh-116195: Improves performance of os.getppid() by using an alternate system API when available. Contributed by vxiiduu.

  • gh-88494: On Windows, time.monotonic() now uses the QueryPerformanceCounter() clock to have a resolution better than 1 us, instead of the GetTickCount64() clock which has a resolution of 15.6 ms. Patch by Victor Stinner.

  • gh-116773: Fix instances of <_overlapped.Overlapped object at 0xXXX> still has pending operation at deallocation, the process may crash.

  • gh-91227: Fix the asyncio ProactorEventLoop implementation so that sending a datagram to an address that is not listening does not prevent receiving any more datagrams.

  • gh-115119: Switched from vendored libmpdecimal code to a separately-hosted external package in the cpython-source-deps repository when building the _decimal module.

C API

  • gh-117642: Fix PEP 737 implementation for %#T and %#N.

  • gh-87193: _PyBytes_Resize() can now be called for bytes objects with reference count > 1, including 1-byte bytes objects. It creates a new bytes object and destroys the old one if it has reference count > 1.

  • gh-117021: Fix integer overflow in PyLong_AsPid() on non-Windows 64-bit platforms.

  • gh-115756: PyCode_GetFirstFree() is an ustable API now and has been renamed to PyUnstable_Code_GetFirstFree(). (Contributed by Bogdan Romanyuk in gh-115781)

  • gh-116869: Add test_cext test: build a C extension to check if the Python C API emits C compiler warnings. Patch by Victor Stinner.

  • gh-116869: Make the C API compatible with -Werror=declaration-after-statement compiler flag again. Patch by Victor Stinner.

  • gh-116936: Add PyType_GetModuleByDef() to the limited C API. Patch by Victor Stinner.

  • gh-116809: Restore removed private _PyErr_ChainExceptions1() function. Patch by Victor Stinner.

  • gh-115754: In the limited C API version 3.13, getting Py_None, Py_False, Py_True, Py_Ellipsis and Py_NotImplemented singletons is now implemented as function calls at the stable ABI level to hide implementation details. Getting these constants still return borrowed references. Patch by Victor Stinner.

  • gh-115754: Add Py_GetConstant() and Py_GetConstantBorrowed() functions to get constants. For example, Py_GetConstant(Py_CONSTANT_ZERO) returns a strong reference to the constant zero. Patch by Victor Stinner.

  • gh-111696: Add support for %T, %T#, %N and %N# formats to PyUnicode_FromFormat(): format the fully qualified name of an object type and of a type: call PyType_GetModuleName(). See PEP 737 for more information. Patch by Victor Stinner.

  • gh-111696: Add PyType_GetModuleName() function to get the type’s module name. Equivalent to getting the type.__module__ attribute. Patch by Eric Snow and Victor Stinner.

  • gh-111696: Add PyType_GetFullyQualifiedName() function to get the type’s fully qualified name. Equivalent to f"{type.__module__}.{type.__qualname__}", or type.__qualname__ if type.__module__ is not a string or is equal to "builtins". Patch by Victor Stinner.

  • gh-85283: The fcntl, grp, pwd, termios, _statistics and _testconsole C extensions are now built with the limited C API. Patch by Victor Stinner.

  • gh-111140: Add additional flags to PyLong_AsNativeBytes() and PyLong_FromNativeBytes() to allow the caller to determine how to handle edge cases around values that fill the entire buffer.

  • gh-113024: Add PyObject_GenericHash() function.

Python 3.13.0 alpha 5

Release date: 2024-03-12

Security

Core and Builtins

  • gh-116604: Respect the status of the garbage collector when indirect calls are made via PyErr_CheckSignals() and the evaluation breaker. Patch by Pablo Galindo

  • gh-112087: list is now compatible with the implementation of PEP 703.

  • gh-116381: Add specialization for CONTAINS_OP.

  • gh-116296: Fix possible refleak in object.__reduce__() internal error handling.

  • gh-115823: Properly calculate error ranges in the parser when raising SyntaxError exceptions caused by invalid byte sequences. Patch by Pablo Galindo

  • gh-115778: Add tierN annotation for instruction definition in interpreter DSL.

  • gh-115733: Fix crash when calling next() on exhausted list iterators.

  • gh-115700: The regen-cases build stage now works on Windows.

  • gh-115347: Fix bug where docstring was replaced by a redundant NOP when Python is run with -OO.

  • gh-115323: Make error message more meaningful for when bytearray.extend() is called with a str object.

  • gh-112175: Every PyThreadState now has its own eval_breaker, allowing specific threads to be interrupted.

Library

Core and Builtins

Library

  • gh-104090: The multiprocessing resource tracker now exits with non-zero status code if a resource leak was detected. It still exits with status code 0 otherwise.

Core and Builtins

  • gh-105858: Improve the constructors for ast nodes. Arguments of list types now default to an empty list if omitted, and optional fields default to None. AST nodes now have an __annotations__ attribute with the expected types of their attributes. Passing unrecognized extra arguments to AST nodes is deprecated and will become an error in Python 3.15. Omitting a required argument to an AST node is deprecated and will become an error in Python 3.15. Patch by Jelle Zijlstra.

  • gh-101860: Expose __name__ attribute on property.

  • gh-96497: Fix incorrect resolution of mangled class variables used in assignment expressions in comprehensions.

Library

  • gh-116600: Fix repr() for global Flag members.

  • gh-116349: platform.java_ver() is deprecated and will be removed in 3.15. It was largely untested, had a confusing API, and was only useful for Jython support.

  • gh-116143: Fix a race in pydoc _start_server, eliminating a window in which _start_server can return a thread that is “serving” but without a docserver set.

  • gh-116127: typing: implement PEP 705 which adds typing.ReadOnly support to typing.TypedDict.

  • gh-116325: typing: raise SyntaxError instead of AttributeError on forward references as empty strings.

  • gh-115957: When asyncio.TaskGroup.create_task is called on an inactive asyncio.TaskGroup, the given coroutine will be closed (which prevents a RuntimeWarning).

  • gh-115978: Disable preadv(), readv(), pwritev(), and writev() on WASI.

    Under wasmtime for WASI 0.2, these functions don’t pass test_posix (https://github.com/bytecodealliance/wasmtime/issues/7830).

  • gh-88352: Fix the computation of the next rollover time in the logging.TimedRotatingFileHandler handler. computeRollover() now always returns a timestamp larger than the specified time and works correctly during the DST change. doRollover() no longer overwrite the already rolled over file, saving from data loss when run at midnight or during repeated time at the DST change.

  • gh-87115: Set __main__.__spec__ to None when running a script with pdb

  • gh-76511: Fix UnicodeEncodeError in email.Message.as_string() that results when a message that claims to be in the ascii character set actually has non-ascii characters. Non-ascii characters are now replaced with the U+FFFD replacement character, like in the replace error handler.

  • gh-89547: Add support for nested typing special forms like Final[ClassVar[int]].

  • gh-65824: Improve the less prompt in pydoc.

  • gh-116040: [Enum] fix by-value calls when second value is falsey; e.g. Cardinal(1, 0)

  • gh-115821: [Enum] Improve error message when calling super().__new__() in custom __new__.

  • gh-85644: Use the XDG_CURRENT_DESKTOP environment variable in webbrowser to check desktop. Prefer it to the deprecated GNOME_DESKTOP_SESSION_ID for GNOME detection.

  • gh-75988: Fixed unittest.mock.create_autospec() to pass the call through to the wrapped object to return the real result.

  • gh-115881: Fix issue where ast.parse() would incorrectly flag conditional context managers (such as with (x() if y else z()): ...) as invalid syntax if feature_version=(3, 8) was passed. This reverts changes to the grammar made as part of gh-94949.

  • gh-115886: Fix silent truncation of the name with an embedded null character in multiprocessing.shared_memory.SharedMemory.

  • gh-115532: Add kernel density estimation to the statistics module.

  • gh-115714: On WASI, the time module no longer get process time using times() or CLOCK_PROCESS_CPUTIME_ID, system API is that is unreliable and is likely to be removed from WASI. The affected clock functions fall back to calling clock().

  • gh-115809: Improve algorithm for computing which rolled-over log files to delete in logging.TimedRotatingFileHandler. It is now reliable for handlers without namer and with arbitrary deterministic namer that leaves the datetime part in the file name unmodified.

  • gh-74668: urllib.parse functions parse_qs() and parse_qsl() now support bytes arguments containing raw and percent-encoded non-ASCII data.

  • gh-67044: csv.writer() now always quotes or escapes '\r' and '\n', regardless of lineterminator value.

  • gh-115712: Restore support of space delimiter with skipinitialspace=True in csv. csv.writer() now quotes empty fields if delimiter is a space and skipinitialspace is true and raises exception if quoting is not possible.

  • gh-112364: Fixed ast.unparse() to handle format_spec with ", ' or \\. Patched by Frank Hoffmann.

  • gh-112997: Stop logging potentially sensitive callback arguments in asyncio unless debug mode is active.

  • gh-114914: Fix an issue where an abandoned StreamWriter would not be garbage collected.

  • gh-111358: Fix a bug in asyncio.BaseEventLoop.shutdown_default_executor() to ensure the timeout passed to the coroutine behaves as expected.

  • gh-115618: Fix improper decreasing the reference count for None argument in property methods getter(), setter() and deleter().

  • gh-112720: Refactor dis.ArgResolver to make it possible to subclass and change the way jump args are interpreted.

  • gh-112006: Fix inspect.unwrap() for types with the __wrapper__ data descriptor. Fix inspect.Signature.from_callable() for builtins classmethod() and staticmethod().

  • gh-101293: Support callables with the __call__() method and types with __new__() and __init__() methods set to class methods, static methods, bound methods, partial functions, and other types of methods and descriptors in inspect.Signature.from_callable().

  • gh-103092: Isolate _lsprof (apply PEP 687).

  • gh-113942: pydoc no longer skips global functions implemented as builtin methods, such as MethodDescriptorType and WrapperDescriptorType.

  • gh-115256: Added DeprecationWarning when accessing the tarfile attribute of TarInfo objects. The attribute is never used internally and is only attached to TarInfos when the tarfile is opened in write-mode, not read-mode. The attribute creates an unnecessary reference cycle which may cause corruption when not closing the handle after writing a tarfile.

  • gh-115197: urllib.request no longer resolves the hostname before checking it against the system’s proxy bypass list on macOS and Windows.

  • gh-113812: DatagramTransport.sendto() will now send zero-length datagrams if called with an empty bytes object. The transport flow control also now accounts for the datagram header when calculating the buffer size.

  • gh-114763: Protect modules loaded with importlib.util.LazyLoader from race conditions when multiple threads try to access attributes before the loading is complete.

  • gh-114709: posixpath.commonpath() now raises a ValueError exception when passed an empty iterable. Previously, IndexError was raised.

    posixpath.commonpath() now raises a TypeError exception when passed None. Previously, ValueError was raised.

  • gh-114610: Fix bug where pathlib.PurePath.with_stem() converted a non-empty path suffix to a stem when given an empty stem argument. It now raises ValueError, just like pathlib.PurePath.with_suffix() does when called on a path with an empty stem, given a non-empty suffix argument.

  • gh-107361: Add ssl.VERIFY_X509_PARTIAL_CHAIN and VERIFY_X509_STRICT to the default SSL context created with ssl.create_default_context().

  • gh-112281: Allow creating union of types for typing.Annotated with unhashable metadata.

  • gh-111775: Fix importlib.resources.simple.ResourceHandle.open() for text mode, added missed stream argument.

  • gh-90095: Make .pdbrc and -c work with any valid pdb commands.

  • gh-107625: Raise configparser.ParsingError from read() and read_file() methods of configparser.ConfigParser if a key without a corresponding value is continued (that is, followed by an indented line).

  • gh-107155: Fix incorrect output of help(x) where x is a lambda function, which has an __annotations__ dictionary attribute with a "return" key.

  • gh-57141: Add option for non-shallow comparisons to filecmp.dircmp like filecmp.cmp(). Original patch by Steven Ward. Enhanced by Tobias Rautenkranz

  • gh-69990: Profile.print_stats() has been improved to accept multiple sort arguments. Patched by Chiu-Hsiang Hsu and Furkan Onder.

  • gh-104061: Add socket.SO_BINDTOIFINDEX constant.

  • gh-60346: Fix ArgumentParser inconsistent with parse_known_args.

  • gh-102389: Add windows_31j to aliases for cp932 codec

  • gh-72249: Always include the module name in the repr() of functools.partial() objects. Patch by Furkan Onder and Anilyka Barry.

  • gh-100985: Update HTTPSConnection to consistently wrap IPv6 Addresses when using a proxy.

  • gh-100884: email: fix misfolding of comma in address-lists over multiple lines in combination with unicode encoding.

  • gh-95782: Fix io.BufferedReader.tell(), io.BufferedReader.seek(), _pyio.BufferedReader.tell(), io.BufferedRandom.tell(), io.BufferedRandom.seek() and _pyio.BufferedRandom.tell() being able to return negative offsets.

  • gh-96310: Fix a traceback in argparse when all options in a mutually exclusive group are suppressed.

  • gh-93205: Fixed a bug in logging.handlers.TimedRotatingFileHandler where multiple rotating handler instances pointing to files with the same name but different extensions would conflict and not delete the correct files.

  • bpo-31116: Add Z85 encoding to base64.

  • bpo-44865: Add missing call to localization function in argparse.

  • bpo-43952: Fix multiprocessing.connection.Listener.accept() to accept empty bytes as authkey. Not accepting empty bytes as key causes it to hang indefinitely.

  • bpo-42125: linecache: get module name from __spec__ if available. This allows getting source code for the __main__ module when a custom loader is used.

  • bpo-41122: Failing to pass arguments properly to functools.singledispatchmethod() now throws a TypeError instead of hitting an index out of bounds internally.

  • bpo-40818: The asyncio REPL now runs sys.__interactivehook__ on startup. The default implementation of sys.__interactivehook__ provides auto-completion to the asyncio REPL. Patch contributed by Rémi Lapeyre.

  • bpo-33775: Add ‘default’ and ‘version’ help text for localization in argparse.

Documentation

Tests

  • gh-71052: Add test exclusions to support running the test suite on Android.

  • gh-71052: Enable test_concurrent_futures on platforms that support threading but not multiprocessing.

  • gh-115796: Make ‘_testinternalcapi.assemble_code_object’ construct the exception table for the code object.

  • gh-115720: Leak tests (-R, --huntrleaks) now show a summary of the number of leaks found in each iteration.

  • gh-115122: Add --bisect option to regrtest test runner: run failed tests with test.bisect_cmd to identify failing tests. Patch by Victor Stinner.

  • gh-115596: Fix ProgramPriorityTests in test_os permanently changing the process priority.

  • gh-115556: On Windows, commas passed in arguments to Tools\buildbot\test.bat and PCbuild\\rt.bat are now properly handled.

  • gh-115420: Fix translation of exception handler targets by _testinternalcapi.optimize_cfg.

  • gh-115376: Fix segfault in _testinternalcapi.compiler_codegen on bad input.

Build

  • gh-116313: Get WASI builds to work under wasmtime 18 w/ WASI 0.2/preview2 primitives.

  • gh-71052: Change Android’s sys.platform from "linux" to "android".

  • gh-116117: Backport libb2’s PR #42 to fix compiling CPython on 32-bit Windows with clang-cl.

  • gh-71052: Fix several Android build issues

  • gh-114099: A testbed project was added to run the test suite on iOS.

  • gh-115350: Fix building ctypes module with -DWIN32_LEAN_AND_MEAN defined

  • gh-111225: Link extension modules against libpython on Android.

  • gh-115737: The install name for libPython is now correctly set for non-framework macOS builds.

  • gh-114099: Makefile targets were added to support compiling an iOS-compatible framework build.

Windows

  • gh-116012: Ensure the value of GetLastError() is preserved across GIL operations.

  • gh-115582: Building extensions intended for free-threaded builds of CPython now require compiling with /DPy_GIL_DISABLED manually when using a regular install. This is expected to change in future releases.

  • gh-115554: The installer now has more strict rules about updating the Python install manager. In general, most users only have a single launcher installed and will see no difference. When multiple launchers have been installed, the option to install the launcher is disabled until all but one have been removed. Downgrading the launcher (which was never allowed) is now more obviously blocked.

  • gh-115543: Python install manager can now detect Python 3.13 when installed from the Microsoft Store, and will install Python 3.12 by default when PYLAUNCHER_ALLOW_INSTALL is set.

macOS

  • gh-116145: Update macOS installer to Tcl/Tk 8.6.14.

IDLE

  • gh-88516: On macOS show a proxy icon in the title bar of editor windows to match platform behaviour.

Tools/Demos

  • gh-100176: Remove outdated Tools/{io,cc,string}bench

  • bpo-45101: Add consistency in usage message IO between 2 versions of python-config.

C API

  • gh-114626: Add again _PyCFunctionFastWithKeywords name, removed in Python 3.13 alpha 4 by mistake. Keep the old private _PyCFunctionFastWithKeywords name (Python 3.7) as an alias to the new public name PyCFunctionFastWithKeywords (Python 3.13a4). Patch by Victor Stinner.

  • gh-111418: Add PyHASH_MODULUS, PyHASH_BITS, PyHASH_INF and PyHASH_IMAG C macros. Patch by Sergey B Kirpichev.

Python 3.13.0 alpha 4

Release date: 2024-02-15

Security

Core and Builtins

  • gh-112087: For an empty reverse iterator for list will be reduced to reversed(). Patch by Donghee Na

  • gh-114570: Add PythonFinalizationError exception. This exception derived from RuntimeError is raised when an operation is blocked during the Python finalization. Patch by Victor Stinner.

  • gh-114695: Add sys._clear_internal_caches(), which clears all internal performance-related caches (and deprecate the less-general sys._clear_type_cache() function).

  • gh-114828: Fix compilation crashes in uncommon code examples using super() inside a comprehension in a class body.

  • gh-112069: Adapt set and frozenset methods to Argument Clinic.

  • gh-115011: Setters for members with an unsigned integer type now support the same range of valid values for objects that has a __index__() method as for int.

  • gh-114887: Changed socket type validation in create_datagram_endpoint() to accept all non-stream sockets. This fixes a regression in compatibility with raw sockets.

  • gh-114944: Fixes a race between PyParkingLot_Park and _PyParkingLot_UnparkAll.

  • gh-113462: Limit the number of versions that a single class can use. Prevents a few wayward classes using up all the version numbers.

  • gh-76763: The chr() builtin function now always raises ValueError for values outside the valid range. Previously it raised OverflowError for very large or small values.

  • gh-114806: No longer specialize calls to classes, if those classes have metaclasses. Fixes bug where the __call__ method of the metaclass was not being called.

  • gh-107944: Improve error message for function calls with bad keyword arguments via getargs

  • gh-112529: The free-threaded build no longer allocates space for the PyGC_Head structure in objects that support cyclic garbage collection. A number of other fields and data structures are used as replacements, including ob_gc_bits, ob_tid, and mimalloc internal data structures.

  • gh-114456: Lower the recursion limit under a debug build of WASI.

  • gh-114083: Compiler applies folding of LOAD_CONST with following instruction in a separate pass before other optimisations. This enables jump threading in certain circumstances.

  • gh-114388: Fix a RuntimeWarning emitted when assign an integer-like value that is not an instance of int to an attribute that corresponds to a C struct member of type T_UINT and T_ULONG. Fix a double RuntimeWarning emitted when assign a negative integer value to an attribute that corresponds to a C struct member of type T_UINT.

  • gh-114265: Compiler propagates line numbers before optimization, leading to more optimization opportunities and removing the need for the guarantee_lineno_for_exits hack.

  • gh-112529: The free-threaded build now has its own thread-safe GC implementation that uses mimalloc to find GC tracked objects. It is non-generational, unlike the existing GC implementation.

  • gh-114050: Fix segmentation fault caused by an incorrect format string in TypeError exception when more than two arguments are passed to int.

  • gh-112354: The END_FOR instruction now pops only one value. This is to better support side exits in loops.

  • gh-113884: Make queue.SimpleQueue thread safe when the GIL is disabled.

  • gh-114058: Implement the foundations of the Tier 2 redundancy eliminator.

  • gh-113939: frame.clear(): Clear frame.f_locals as well, and not only the fast locals. This is relevant once frame.f_locals was accessed, which would contain also references to all the locals.

  • gh-112050: Convert collections.deque to use Argument Clinic.

  • gh-112050: Make methods on collections.deque thread-safe when the GIL is disabled.

  • gh-113464: Add an option (--enable-experimental-jit for configure-based builds or --experimental-jit for PCbuild-based ones) to build an experimental just-in-time compiler, based on copy-and-patch

  • gh-113055: Make interp->obmalloc a pointer. For interpreters that share state with the main interpreter, this points to the same static memory structure. For interpreters with their own obmalloc state, it is heap allocated. Add free_obmalloc_arenas() which will free the obmalloc arenas and radix tree structures for interpreters with their own obmalloc state.

  • gh-55664: Add warning when creating type using a namespace dictionary with non-string keys. Patched by Daniel Urban and Furkan Onder.

  • gh-104530: Use native Win32 condition variables.

Library

  • gh-115392: Fix a bug in doctest where incorrect line numbers would be reported for decorated functions.

  • gh-114563: Fix several format() bugs when using the C implementation of Decimal: * memory leak in some rare cases when using the z format option (coerce negative 0) * incorrect output when applying the z format option to type F (fixed-point with capital NAN / INF) * incorrect output when applying the # format option (alternate form)

  • gh-102840: Fix confused traceback when floordiv, mod, or divmod operations happens between instances of fractions.Fraction and complex.

  • gh-115165: Most exceptions are now ignored when attempting to set the __orig_class__ attribute on objects returned when calling typing generic aliases (including generic aliases created using typing.Annotated). Previously only AttributeError was ignored. Patch by Dave Shawley.

  • gh-112903: Fix “issubclass() arg 1 must be a class” errors in certain cases of multiple inheritance with generic aliases (regression in early 3.13 alpha releases).

  • gh-115133: Fix tests for XMLPullParser with Expat 2.6.0.

  • gh-115059: io.BufferedRandom.read1() now flushes the underlying write buffer.

  • gh-79382: Trailing ** no longer allows to match files and non-existing paths in recursive glob().

  • gh-67837: Avoid race conditions in the creation of directories during concurrent extraction in tarfile and zipfile.

  • gh-115060: Speed up pathlib.Path.glob() by removing redundant regex matching.

  • gh-97928: Partially revert the behavior of tkinter.Text.count(). By default it preserves the behavior of older Python versions, except that setting wantobjects to 0 no longer has effect. Add a new parameter return_ints: specifying return_ints=True makes Text.count() always returning the single count as an integer instead of a 1-tuple or None.

  • gh-114628: When csv.Error is raised when handling TypeError, do not print the TypeError traceback.

  • gh-85984: Added _POSIX_VDISABLE from C’s <unistd.h> to termios.

  • gh-114965: Update bundled pip to 24.0

  • gh-114959: tarfile no longer ignores errors when trying to extract a directory on top of a file.

  • gh-114894: Add array.array.clear().

  • gh-114071: Support tuple subclasses using auto() for enum member value.

  • gh-109475: Fix support of explicit option value “–” in argparse (e.g. --option=--).

  • gh-49766: Fix date-datetime comparison. Now the special comparison methods like __eq__ and __lt__ return NotImplemented if one of comparands is date and other is datetime instead of ignoring the time part and the time zone or forcefully return “not equal” or raise TypeError. It makes comparison of date and datetime subclasses more symmetric and allows to change the default behavior by overriding the special comparison methods in subclasses.

  • gh-110190: Fix ctypes structs with array on Windows ARM64 platform by setting MAX_STRUCT_SIZE to 32 in stgdict. Patch by Diego Russo

  • gh-114678: Ensure that deprecation warning for ‘N’ specifier in Decimal format is not raised for cases where ‘N’ appears in other places in the format specifier. Based on patch by Stefan Krah.

  • gh-70303: Return both files and directories from pathlib.Path.glob() if a pattern ends with “**”. Previously only directories were returned.

  • gh-109653: Improve import time of importlib.metadata and email.utils.

  • gh-113280: Fix a leak of open socket in rare cases when error occurred in ssl.SSLSocket creation.

  • gh-77749: email.policy.EmailPolicy.fold() now always encodes non-ASCII characters in headers if utf8 is false.

  • gh-83383: Synchronization of the dbm.dumb database is now no-op if there was no modification since opening or last synchronization. The directory file for a newly created empty dbm.dumb database is now created immediately after opening instead of deferring this until synchronizing or closing.

  • gh-91602: Add filter keyword-only parameter to sqlite3.Connection.iterdump() for filtering database objects to dump. Patch by Mariusz Felisiak.

  • gh-112451: Prohibit subclassing pure-Python datetime.timezone. This is consistent with C-extension implementation. Patch by Mariusz Felisiak.

  • gh-69893: Add the close() method for the iterator returned by xml.etree.ElementTree.iterparse().

  • gh-109653: Reduce the import time of threading module by ~50%. Patch by Daniel Hollas.

  • gh-114492: Make the result of termios.tcgetattr() reproducible on Alpine Linux. Previously it could leave a random garbage in some fields.

  • gh-114315: Make threading.Lock a real class, not a factory function. Add __new__ to _thread.lock type.

  • gh-100414: Add dbm.sqlite3 as a backend to dbm, and make it the new default dbm backend. Patch by Raymond Hettinger and Erlend E. Aasland.

  • gh-113267: Revert changes in gh-106584 which made calls of TestResult methods startTest() and stopTest() unbalanced.

  • gh-75128: Ignore an OSError in asyncio.BaseEventLoop.create_server() when IPv6 is available but the interface cannot actually support it.

  • gh-114423: _DummyThread entries in threading._active are now automatically removed when the related thread dies.

  • gh-114257: Dismiss the FileNotFound error in ctypes.util.find_library() and just return None on Linux.

  • gh-114321: Expose more platform specific constants in the fcntl module on Linux, macOS, FreeBSD and NetBSD.

  • gh-114328: The tty.setcbreak() and new tty.cfmakecbreak() no longer clears the terminal input ICRLF flag. This fixes a regression introduced in 3.12 that no longer matched how OSes define cbreak mode in their stty(1) manual pages.

  • gh-114281: Remove type hints from Lib/asyncio/staggered.py. The annotations in the typeshed project should be used instead.

  • gh-101438: Avoid reference cycle in ElementTree.iterparse. The iterator returned by ElementTree.iterparse may hold on to a file descriptor. The reference cycle prevented prompt clean-up of the file descriptor if the returned iterator was not exhausted.

  • gh-114198: The signature for the __replace__ method on dataclasses now has the first argument named self, rather than obj.

  • gh-104522: OSError raised when run a subprocess now only has filename attribute set to cwd if the error was caused by a failed attempt to change the current directory.

  • gh-114149: Enum: correctly handle tuple subclasses in custom __new__.

  • gh-83648: Support deprecation of options, positional arguments and subcommands in argparse.

  • gh-114087: Speed up dataclasses.asdict up to 1.35x.

  • gh-109534: Fix a reference leak in asyncio.selector_events.BaseSelectorEventLoop when SSL handshakes fail. Patch contributed by Jamie Phan.

  • gh-79634: Accept path-like objects as patterns in pathlib.Path.glob() and rglob().

  • gh-112202: Ensure that a asyncio.Condition.notify() call does not get lost if the awakened Task is simultaneously cancelled or encounters any other error.

  • gh-113951: Fix the behavior of tag_unbind() methods of tkinter.Text and tkinter.Canvas classes with three arguments. Previously, widget.tag_unbind(tag, sequence, funcid) destroyed the current binding for sequence, leaving sequence unbound, and deleted the funcid command. Now it removes only funcid from the binding for sequence, keeping other commands, and deletes the funcid command. It leaves sequence unbound only if funcid was the last bound command.

  • gh-97959: Fix rendering class methods, bound methods, method and function aliases in pydoc. Class methods no longer have “method of builtins.type instance” note. Corresponding notes are now added for class and unbound methods. Method and function aliases now have references to the module or the class where the origin was defined if it differs from the current. Bound methods are now listed in the static methods section. Methods of builtin classes are now supported as well as methods of Python classes.

  • gh-113796: Add more validation checks in the csv.Dialect constructor. ValueError is now raised if the same character is used in different roles.

  • gh-113732: Fix support of QUOTE_NOTNULL and QUOTE_STRINGS in csv.reader().

  • gh-113225: Speed up pathlib.Path.walk() by using os.DirEntry.path where possible.

  • gh-89039: When replace() method is called on a subclass of datetime, date or time, properly call derived constructor. Previously, only the base class’s constructor was called.

    Also, make sure to pass non-zero fold values when creating subclasses in various methods. Previously, fold was silently ignored.

  • gh-112919: Speed-up datetime.datetime.replace(), datetime.date.replace() and datetime.time.replace().

  • gh-59013: Set breakpoint on the first executable line of the function, instead of the line of function definition when the user do break func using pdb

  • gh-112343: Improve handling of pdb convenience variables to avoid replacing string contents.

  • gh-112240: Add option to calendar module CLI to specify the weekday to start each week. Patch by Steven Ward.

  • gh-111741: Recognise image/webp as a standard format in the mimetypes module.

  • gh-43457: Fix the tkinter widget method wm_attributes(). It now accepts the attribute name without the minus prefix to get window attributes and allows to specify attributes and values to set as keyword arguments. Add new optional keyword argument return_python_dict: calling w.wm_attributes(return_python_dict=True) returns the attributes as a dict instead of a tuple. Calling w.wm_attributes() now returns a tuple instead of string if wantobjects was set to 0.

  • gh-82626: Many functions now emit a warning if a boolean value is passed as a file descriptor argument.

  • gh-111051: Added check for file modification during debugging with pdb

  • gh-110345: Show the Tcl/Tk patchlevel (rather than version) in tkinter._test().

  • gh-38807: Fix race condition in trace. Instead of checking if a directory exists and creating it, directly call os.makedirs() with the kwarg exist_ok=True.

  • gh-75705: Set unixfrom envelope in mailbox.mbox and mailbox.MMDF.

  • gh-106233: Fix stacklevel in InvalidTZPathWarning during zoneinfo module import.

  • gh-105102: Allow ctypes.Union to be nested in ctypes.Structure when the system endianness is the opposite of the classes.

  • gh-104282: Fix null pointer dereference in lzma._decode_filter_properties() due to improper handling of BCJ filters with properties of zero length. Patch by Radislav Chugunov.

  • gh-96471: Add queue.Queue termination with shutdown().

  • gh-101599: Changed argparse flag options formatting to remove redundancy.

  • gh-85984: Add POSIX pseudo-terminal functions os.posix_openpt(), os.grantpt(), os.unlockpt(), and os.ptsname().

  • gh-102512: When os.fork() is called from a foreign thread (aka _DummyThread), the type of the thread in a child process is changed to _MainThread. Also changed its name and daemonic status, it can be now joined.

  • gh-88569: Add os.path.isreserved(), which identifies reserved pathnames such as “NUL”, “AUX” and “CON”. This function is only available on Windows.

    Deprecate pathlib.PurePath.is_reserved().

  • bpo-38364: The inspect functions isgeneratorfunction, iscoroutinefunction, isasyncgenfunction now support functools.partialmethod wrapped functions the same way they support functools.partial.

Documentation

  • gh-115233: Fix an example for LoggerAdapter in the Logging Cookbook.

  • gh-114123: Move the csv module docstring to the csv module instead of reexporting it from the internal _csv module, and remove __doc__ from csv.__all__.

    Move csv.__version__ to the csv module instead of reexporting it from the internal _csv module, and remove __version__ from csv.__all__.

Tests

  • gh-114099: Added test exclusions required to run the test suite on iOS.

  • gh-105089: Fix test.test_zipfile.test_core.TestWithDirectory.test_create_directory_with_write test in AIX by doing a bitwise AND of 0xFFFF on mode , so that it will be in sync with zinfo.external_attr

Build

  • gh-115167: Avoid vendoring vcruntime140_threads.dll when building with Visual Studio 2022 version 17.8.

  • gh-113632: Promote WASI to a tier 2 platform and drop Emscripten from tier 3 in configure.ac.

  • gh-114099: configure and Makefile were refactored to accommodate framework builds on Apple platforms other than macOS.

  • gh-114875: Add getgrent() as a prerequisite for building the grp module.

Windows

  • gh-115049: Fixes py.exe launcher failing when run as users without user profiles.

  • gh-115009: Update Windows installer to use SQLite 3.45.1.

  • gh-109991: Update Windows build to use OpenSSL 3.0.13.

  • gh-111239: Update Windows builds to use zlib v1.3.1.

  • gh-100107: The py.exe launcher will no longer attempt to run the Microsoft Store redirector when launching a script containing a /usr/bin/env shebang

  • gh-112984: Adds free-threaded binaries to Windows installer as an optional component.

  • gh-89240: Allows multiprocessing to create pools of greater than 62 processes.

macOS

  • gh-115009: Update macOS installer to use SQLite 3.45.1.

  • gh-109991: Update macOS installer to use OpenSSL 3.0.13.

  • gh-114490: Add Mach-O linkage support for platform.architecture().

  • gh-87804: On macOS the result of os.statvfs and os.fstatvfs now correctly report the size of very large disks, in previous versions the reported number of blocks was wrong for disks with at least 2**32 blocks.

IDLE

  • gh-96905: In idlelib code, stop redefining built-ins ‘dict’ and ‘object’.

  • gh-103820: Revise IDLE bindings so that events from mouse button 4/5 on non-X11 windowing systems (i.e. Win32 and Aqua) are not mistaken for scrolling.

Tools/Demos

  • gh-113516: Don’t set LDSHARED when building for WASI.

  • gh-109991: Update GitHub CI workflows to use OpenSSL 3.0.13 and multissltests to use 1.1.1w, 3.0.13, 3.1.5, and 3.2.1.

  • gh-115015: Fix a bug in Argument Clinic that generated incorrect code for methods with no parameters that use the METH_METHOD | METH_FASTCALL | METH_KEYWORDS calling convention. Only the positional parameter count was checked; any keyword argument passed would be silently accepted.

C API

Python 3.13.0 alpha 3

Release date: 2024-01-17

Security

  • gh-113659: Skip .pth files with names starting with a dot or hidden file attribute.

  • gh-112302: Created a Software Bill-of-Materials document and tooling for tracking dependencies.

Core and Builtins

  • gh-107901: Compiler duplicates basic blocks that have an eval breaker check, no line number, and multiple predecessors.

  • gh-107901: A jump leaving an exception handler back to normal code no longer checks the eval breaker.

  • gh-113655: Set the C recursion limit to 4000 on Windows, and 10000 on Linux/OSX. This seems to be near the sweet spot to maintain safety, but not compromise backwards compatibility.

  • gh-113710: Add typed stack effects to the interpreter DSL, along with various instruction annotations.

  • gh-77046: On Windows, file descriptors wrapping Windows handles are now created non inheritable by default (PEP 446). Patch by Zackery Spytz and Victor Stinner.

  • gh-113853: Guarantee that all executors make progress. This then guarantees that tier 2 execution always makes progress.

  • gh-113753: Fix an issue where the finalizer of PyAsyncGenASend objects might not be called if they were allocated from a free list.

  • gh-107901: Compiler changed so that synthetic jumps which are not at loop end no longer check the eval breaker.

  • gh-113703: Fix a regression in the codeop module that was causing it to incorrectly identify incomplete f-strings. Patch by Pablo Galindo

  • gh-89811: Check for a valid tp_version_tag before performing bytecode specializations that rely on this value being usable.

  • gh-111488: Changed error message in case of no ‘in’ keyword after ‘for’ in list comprehensions

  • gh-113657: Fix an issue that caused important instruction pointer updates to be optimized out of tier two traces.

  • gh-113603: Fixed bug where a redundant NOP is not removed, causing an assertion to fail in the compiler in debug mode.

  • gh-113602: Fix an error that was causing the parser to try to overwrite existing errors and crashing in the process. Patch by Pablo Galindo

  • gh-113486: No longer issue spurious PY_UNWIND events for optimized calls to classes.

  • gh-113297: Fix segfault in the compiler on with statement with 19 context managers.

  • gh-113212: Improve super error messages.

  • gh-111375: Only use NULL in the exception stack to indicate an exception was handled. Patch by Carey Metcalfe.

  • gh-112215: Increase the C recursion limit by a factor of 3 for non-debug builds, except for webassembly and s390 platforms which are unchanged. This mitigates some regressions in 3.12 with deep recursion mixing builtin (C) and Python code.

  • gh-113054: Fixed bug where a redundant NOP is not removed, causing an assertion to fail in the compiler in debug mode.

  • gh-106905: Use per AST-parser state rather than global state to track recursion depth within the AST parser to prevent potential race condition due to simultaneous parsing.

    The issue primarily showed up in 3.11 by multithreaded users of ast.parse(). In 3.12 a change to when garbage collection can be triggered prevented the race condition from occurring.

  • gh-108866: Change the API and contract of _PyExecutorObject to return the next_instr pointer, instead of the frame, and to always execute at least one instruction.

  • gh-90350: Optimize builtin functions min() and max().

  • gh-112943: Correctly compute end column offsets for multiline tokens in the tokenize module. Patch by Pablo Galindo

  • gh-112125: Fix None.__ne__(None) returning NotImplemented instead of False.

  • gh-74616: input() now raises a ValueError when output on the terminal if the prompt contains embedded null characters instead of silently truncating it.

  • gh-112716: Fix SystemError in the import statement and in __reduce__() methods of builtin types when __builtins__ is not a dict.

  • gh-112730: Use color to highlight error locations in tracebacks. Patch by Pablo Galindo

  • gh-112625: Fixes a bug where a bytearray object could be cleared while iterating over an argument in the bytearray.join() method that could result in reading memory after it was freed.

  • gh-112660: Do not clear unexpected errors during formatting error messages for ImportError and AttributeError for modules.

  • gh-105967: Workaround a bug in Apple’s macOS platform zlib library where zlib.crc32() and binascii.crc32() could produce incorrect results on multi-gigabyte inputs. Including when using zipfile on zips containing large data.

  • gh-95754: Provide a better error message when accessing invalid attributes on partially initialized modules. The origin of the module being accessed is now included in the message to help with the common issue of shadowing other modules.

  • gh-112217: Add check for the type of __cause__ returned from calling the type T in raise from T.

  • gh-111058: Change coro.cr_frame/gen.gi_frame to return None after the coroutine/generator has been closed. This fixes a bug where getcoroutinestate() and getgeneratorstate() return the wrong state for a closed coroutine/generator.

  • gh-112388: Fix an error that was causing the parser to try to overwrite tokenizer errors. Patch by pablo Galindo

  • gh-112387: Fix error positions for decoded strings with backwards tokenize errors. Patch by Pablo Galindo

  • gh-99606: Make code generated for an empty f-string identical to the code of an empty normal string.

  • gh-112367: Avoid undefined behaviour when using the perf trampolines by not freeing the code arenas until shutdown. Patch by Pablo Galindo

  • gh-112320: The Tier 2 translator now tracks the confidence level for staying “on trace” (i.e. not exiting back to the Tier 1 interpreter) for branch instructions based on the number of bits set in the branch “counter”. Trace translation ends when the confidence drops below 1/3rd.

  • gh-109598: PyComplex_RealAsDouble()/PyComplex_ImagAsDouble() now tries to convert an object to a complex instance using its __complex__() method before falling back to the __float__() method. Patch by Sergey B Kirpichev.

  • gh-94606: Fix UnicodeEncodeError when email.message.get_payload() reads a message with a Unicode surrogate character and the message content is not well-formed for surrogateescape encoding. Patch by Sidney Markowitz.

  • bpo-21861: Use the object’s actual class name in _io.FileIO.__repr__(), _io._WindowsConsoleIO() and _io.TextIOWrapper.__repr__(), to make these methods subclass friendly.

  • bpo-45369: Remove LibreSSL workarounds as per PEP 644.

  • bpo-34392: Added sys._is_interned().

Library

  • gh-114077: Fix possible OverflowError in socket.socket.sendfile() when pass count larger than 2 GiB on 32-bit platform.

  • gh-111803: plistlib now supports loading more deeply nested lists in binary format.

  • gh-114014: Fixed a bug in fractions.Fraction where an invalid string using d in the decimals part creates a different error compared to other invalid letters/characters. Patch by Jeremiah Gabriel Pascual.

  • gh-108364: sqlite3.Connection.iterdump() now ensures that foreign key support is disabled before dumping the database schema, if there is any foreign key violation. Patch by Erlend E. Aasland and Mariusz Felisiak.

  • gh-113971: The zipfile.ZipInfo previously protected ._compresslevel attribute has been made public as .compress_level with the old _compresslevel name remaining available as a property to retain compatibility.

  • gh-113877: Fix tkinter method winfo_pathname() on 64-bit Windows.

  • gh-113868: Added mmap.MAP_NORESERVE, mmap.MAP_NOEXTEND, mmap.MAP_HASSEMAPHORE, mmap.MAP_NOCACHE, mmap.MAP_JIT, mmap.MAP_RESILIENT_CODESIGN, mmap.MAP_RESILIENT_MEDIA, mmap.MAP_32BIT, mmap.MAP_TRANSLATED_ALLOW_EXECUTE, mmap.MAP_UNIX03 and mmap.MAP_TPRO. All of them are mmap(2) flags on macOS.

  • gh-113848: asyncio.TaskGroup() and asyncio.timeout() context managers now handle CancelledError subclasses as well as exact CancelledError.

  • gh-113661: unittest runner: Don’t exit 5 if tests were skipped. The intention of exiting 5 was to detect issues where the test suite wasn’t discovered at all. If we skipped tests, it was correctly discovered.

  • gh-96037: Insert TimeoutError in the context of the exception that was raised during exiting an expired asyncio.timeout() block.

  • gh-113781: Silence unraisable AttributeError when warnings are emitted during Python finalization.

  • gh-113238: Add Anchor to importlib.resources (in order for the code to comply with the documentation)

  • gh-111693: asyncio.Condition.wait() now re-raises the same CancelledError instance that may have caused it to be interrupted. Fixed race condition in asyncio.Semaphore.acquire() when interrupted with a CancelledError.

  • gh-113791: Add CLOCK_MONOTONIC_RAW_APPROX and CLOCK_UPTIME_RAW_APPROX to time on macOS. These are clocks available on macOS 10.12 or later.

  • gh-112932: Restore the ability for zipfile to extractall from zip files with a “/” directory entry in them as is commonly added to zips by some wiki or bug tracker data exporters.

  • gh-113568: Raise deprecation warnings from pathlib.PurePath and not its private base class PurePathBase.

  • gh-113594: Fix UnicodeEncodeError in email when re-fold lines that contain unknown-8bit encoded part followed by non-unknown-8bit encoded part.

  • gh-113538: In asyncio.StreamReaderProtocol.connection_made(), there is callback that logs an error if the task wrapping the “connected callback” fails. This callback would itself fail if the task was cancelled. Prevent this by checking whether the task was cancelled first. If so, close the transport but don’t log an error.

  • gh-113626: Add support for the allow_code argument in the marshal module. Passing allow_code=False prevents serialization and de-serialization of code objects which is incompatible between Python versions.

  • gh-85567: Fix resource warnings for unclosed files in pickle and pickletools command line interfaces.

  • gh-113537: Support loads str in plistlib.loads().

  • gh-89850: Add default implementations of pickle.Pickler.persistent_id() and pickle.Unpickler.persistent_load() methods in the C implementation. Calling super().persistent_id() and super().persistent_load() in subclasses of the C implementation of pickle.Pickler and pickle.Unpickler classes no longer causes infinite recursion.

  • gh-113569: Indicate if there were no actual calls in unittest assert_has_calls() failure.

  • gh-101225: Increase the backlog for multiprocessing.connection.Listener objects created by multiprocessing.manager and multiprocessing.resource_sharer to significantly reduce the risk of getting a connection refused error when creating a multiprocessing.connection.Connection to them.

  • gh-113568: Raise audit events from pathlib.Path and not its private base class PathBase.

  • gh-113543: Make sure that webbrowser.MacOSXOSAScript sends webbrowser.open audit event.

  • gh-113028: When a second reference to a string appears in the input to pickle, and the Python implementation is in use, we are guaranteed that a single copy gets pickled and a single object is shared when reloaded. Previously, in protocol 0, when a string contained certain characters (e.g. newline) it resulted in duplicate objects.

  • gh-113421: Fix multiprocessing logger for %(filename)s.

  • gh-111784: Fix segfaults in the _elementtree module. Fix first segfault during deallocation of _elementtree.XMLParser instances by keeping strong reference to pyexpat module in module state for capsule lifetime. Fix second segfault which happens in the same deallocation process by keeping strong reference to _elementtree module in XMLParser structure for _elementtree module lifetime.

  • gh-113407: Fix import of unittest.mock when CPython is built without docstrings.

  • gh-113320: Fix regression in Python 3.12 where Protocol classes that were not marked as runtime-checkable would be unnecessarily introspected, potentially causing exceptions to be raised if the protocol had problematic members. Patch by Alex Waygood.

  • gh-53502: Add a new option aware_datetime in plistlib to loads or dumps aware datetime.

  • gh-113358: Fix rendering tracebacks with exceptions with a broken __getattr__

  • gh-113214: Fix an AttributeError during asyncio SSL protocol aborts in SSL-over-SSL scenarios.

  • gh-113246: Update bundled pip to 23.3.2.

  • gh-87264: Fixed tarfile list() method to show file type.

  • gh-112182: asyncio.futures.Future.set_exception() now transforms StopIteration into RuntimeError instead of hanging or other misbehavior. Patch contributed by Jamie Phan.

  • gh-113225: Speed up pathlib.Path.glob() by using os.DirEntry.path where possible.

  • gh-113149: Improve error message when a JSON array or object contains a trailing comma. Patch by Carson Radtke.

  • gh-113117: The subprocess module can now use the os.posix_spawn() function with close_fds=True on platforms where posix_spawn_file_actions_addclosefrom_np is available. Patch by Jakub Kulik.

  • gh-113199: Make http.client.HTTPResponse.read1 and http.client.HTTPResponse.readline close IO after reading all data when content length is known. Patch by Illia Volochii.

  • gh-113191: Add support of os.fchmod() and a file descriptor in os.chmod() on Windows.

  • gh-113188: Fix shutil.copymode() and shutil.copystat() on Windows. Previously they worked differently if dst is a symbolic link: they modified the permission bits of dst itself rather than the file it points to if follow_symlinks is true or src is not a symbolic link, and did not modify the permission bits if follow_symlinks is false and src is a symbolic link.

  • gh-113119: os.posix_spawn() now accepts env=None, which makes the newly spawned process use the current process environment. Patch by Jakub Kulik.

  • gh-113202: Add a strict option to batched() in the itertools module.

  • gh-61648: Detect line numbers of properties in doctests.

  • gh-113175: Sync with importlib_metadata 7.0, including improved type annotations, fixed issue with symlinked packages in package_distributions, added EntryPoints.__repr__, introduced the diagnose script, added Distribution.origin property, and removed deprecated EntryPoint access by numeric index (tuple behavior).

  • gh-59616: Add support of os.lchmod() and the follow_symlinks argument in os.chmod() on Windows. Note that the default value of follow_symlinks in os.lchmod() is False on Windows.

  • gh-112559: signal.signal() and signal.getsignal() no longer call repr on callable handlers. asyncio.run() and asyncio.Runner.run() no longer call repr on the task results. Patch by Yilei Yang.

  • gh-112962: dis module functions add cache information to the Instruction instance rather than creating fake Instruction instances to represent the cache entries.

  • gh-112989: Reduce overhead to connect sockets with asyncio SelectorEventLoop.

  • gh-112970: Use closefrom() on Linux where available (e.g. glibc-2.34), rather than only FreeBSD.

  • gh-110190: Fix ctypes structs with array on PPC64LE platform by setting MAX_STRUCT_SIZE to 64 in stgdict. Patch by Diego Russo.

  • gh-112540: The statistics.geometric_mean() function now returns zero for datasets containing a zero. Formerly, it would raise an exception.

  • gh-87286: Added LOG_FTP, LOG_NETINFO, LOG_REMOTEAUTH, LOG_INSTALL, LOG_RAS, and LOG_LAUNCHD tot the syslog module, all of them constants on used on macOS.

  • gh-112800: Fix asyncio SubprocessTransport.close() not to throw PermissionError when used with setuid executables.

  • gh-51944: Add the following constants to the termios module. These values are present in macOS system headers: ALTWERASE, B14400, B28800, B7200, B76800, CCAR_OFLOW, CCTS_OFLOW, CDSR_OFLOW, CDTR_IFLOW, CIGNORE, CRTS_IFLOW, EXTPROC, IUTF8, MDMBUF, NL2, NL3, NOKERNINFO, ONOEOT, OXTABS, VDSUSP, VSTATUS.

  • gh-79325: Fix an infinite recursion error in tempfile.TemporaryDirectory() cleanup on Windows.

  • gh-94692: shutil.rmtree() now only catches OSError exceptions. Previously a symlink attack resistant version of shutil.rmtree() could ignore or pass to the error handler arbitrary exception when invalid arguments were provided.

  • gh-112736: The use of del-safe symbols in subprocess was refactored to allow for use in cross-platform build environments.

  • gh-112727: Speed up pathlib.Path.absolute(). Patch by Barney Gale.

  • gh-74690: Speedup issubclass() checks against simple runtime-checkable protocols by around 6%. Patch by Alex Waygood.

  • gh-74690: Speedup isinstance() checks by roughly 20% for runtime-checkable protocols that only have one callable member. Speedup issubclass() checks for these protocols by roughly 10%. Patch by Alex Waygood.

  • gh-112645: Remove deprecation error on passing onerror to shutil.rmtree().

  • gh-112640: Add kwdefaults parameter to types.FunctionType to set default keyword argument values.

  • gh-112622: Ensure name parameter is passed to event loop in asyncio.create_task().

  • gh-112618: Fix a caching bug relating to typing.Annotated. Annotated[str, True] is no longer identical to Annotated[str, 1].

  • gh-112334: Fixed a performance regression in 3.12’s subprocess on Linux where it would no longer use the fast-path vfork() system call when it could have due to a logic bug, instead falling back to the safe but slower fork().

    Also fixed a second 3.12.0 potential security bug. If a value of extra_groups=[] was passed to subprocess.Popen or related APIs, the underlying setgroups(0, NULL) system call to clear the groups list would not be made in the child process prior to exec().

    This was identified via code inspection in the process of fixing the first bug.

  • gh-110190: Fix ctypes structs with array on Arm platform by setting MAX_STRUCT_SIZE to 32 in stgdict. Patch by Diego Russo.

  • gh-81194: Fix a crash in socket.if_indextoname() with specific value (UINT_MAX). Fix an integer overflow in socket.if_indextoname() on 64-bit non-Windows platforms.

  • gh-112578: Fix a spurious RuntimeWarning when executing the zipfile module.

  • gh-112516: Update the bundled copy of pip to version 23.3.1.

  • gh-112510: Add readline.backend for the backend readline uses (editline or readline)

  • gh-112328: [Enum] Make EnumDict, EnumDict.member_names, EnumType._add_alias_ and EnumType._add_value_alias_ public.

  • gh-112509: Fix edge cases that could cause a key to be present in both the __required_keys__ and __optional_keys__ attributes of a typing.TypedDict. Patch by Jelle Zijlstra.

  • gh-101336: Add keep_alive keyword parameter for AbstractEventLoop.create_server() and BaseEventLoop.create_server().

  • gh-63284: Added support for TLS-PSK (pre-shared key) mode to the ssl module.

  • gh-112414: Fix regression in Python 3.12 where calling repr() on a module that had been imported using a custom loader could fail with AttributeError. Patch by Alex Waygood.

  • gh-112358: Revert change to struct.Struct initialization that broke some cases of subclassing.

  • gh-112405: Optimize pathlib.PurePath.relative_to(). Patch by Alex Waygood.

  • gh-94722: Fix bug where comparison between instances of DocTest fails if one of them has None as its lineno.

  • gh-112361: Speed up a small handful of pathlib methods by removing some temporary objects.

  • gh-112345: Improve error message when trying to call issubclass() against a typing.Protocol that has non-method members. Patch by Randolf Scholz.

  • gh-112137: Change dis output to display no-lineno as “–” instead of “None”.

  • gh-112332: Deprecate the exc_type field of traceback.TracebackException. Add exc_type_str to replace it.

  • gh-81620: Add extra tests for random.binomialvariate()

  • gh-112292: Fix a crash in readline when imported from a sub interpreter. Patch by Anthony Shaw

  • gh-77621: Slightly improve the import time of the pathlib module by deferring some imports. Patch by Barney Gale.

  • gh-112137: Change dis output to display logical labels for jump targets instead of offsets.

  • gh-112139: Add Signature.format() to format signatures to string with extra options. And use it in pydoc to render more readable signatures that have new lines between parameters.

  • gh-112105: Make readline.set_completer_delims() work with libedit

  • gh-106922: Display multiple lines with traceback when errors span multiple lines.

  • gh-111874: When creating a typing.NamedTuple class, ensure __set_name__() is called on all objects that define __set_name__ and exist in the values of the NamedTuple class’s class dictionary. Patch by Alex Waygood.

  • gh-68166: Add support of the “vsapi” element type in tkinter.ttk.Style.element_create().

  • gh-110275: Named tuple’s methods _replace() and __replace__() now raise TypeError instead of ValueError for invalid keyword arguments.

  • gh-99367: Do not mangle sys.path[0] in pdb if safe_path is set

  • gh-111615: Fix a regression caused by a fix to gh-93162 whereby you couldn’t configure a QueueHandler without specifying handlers.

  • gh-75666: Fix the behavior of tkinter widget’s unbind() method with two arguments. Previously, widget.unbind(sequence, funcid) destroyed the current binding for sequence, leaving sequence unbound, and deleted the funcid command. Now it removes only funcid from the binding for sequence, keeping other commands, and deletes the funcid command. It leaves sequence unbound only if funcid was the last bound command.

  • gh-67790: Implement basic formatting support (minimum width, alignment, fill) for fractions.Fraction.

  • gh-111049: Fix crash during garbage collection of the io.BytesIO buffer object.

  • gh-102980: Redirect the output of interact command of pdb to the same channel as the debugger. Add tests and improve docs.

  • gh-102988: email.utils.getaddresses() and email.utils.parseaddr() now return ('', '') 2-tuples in more situations where invalid email addresses are encountered instead of potentially inaccurate values. Add optional strict parameter to these two functions: use strict=False to get the old behavior, accept malformed inputs. getattr(email.utils, 'supports_strict_parsing', False) can be use to check if the strict parameter is available. Patch by Thomas Dwyer and Victor Stinner to improve the CVE 2023-27043 fix.

  • gh-52161: cmd.Cmd.do_help() now cleans docstrings with inspect.cleandoc() before writing them. Patch by Filip Łapkiewicz.

  • gh-82300: Add track parameter to multiprocessing.shared_memory.SharedMemory that allows using shared memory blocks without having to register with the POSIX resource tracker that automatically releases them upon process exit.

  • gh-110109: Add private pathlib._PurePathBase class: a base class for pathlib.PurePath that omits certain magic methods. It may be made public (along with _PathBase) in future.

  • gh-109858: Protect zipfile from “quoted-overlap” zipbomb. It now raises BadZipFile when try to read an entry that overlaps with other entry or central directory.

  • gh-109786: Fix possible reference leaks and crash when re-enter the __next__() method of itertools.pairwise.

  • gh-91539: Small (10 - 20%) and trivial performance improvement of urllib.request.getproxies_environment(), typically useful when there are many environment variables to go over.

  • gh-103363: Add follow_symlinks keyword-only argument to pathlib.Path.owner() and group(), defaulting to True.

  • gh-102130: Support tab completion in cmd for editline.

  • gh-99437: runpy.run_path() now decodes path-like objects, making sure __file__ and sys.argv[0] of the module being run are always strings.

  • gh-104003: Add warnings.deprecated(), a decorator to mark deprecated functions to static type checkers and to warn on usage of deprecated classes and functions. See PEP 702. Patch by Jelle Zijlstra.

  • gh-103708: Make hardcoded python name, a configurable parameter so that different implementations of python can override it instead of making huge diffs in sysconfig.py

  • gh-66515: mailbox.MH now supports folders that do not contain a .mh_sequences file (e.g. Claws Mail IMAP-cache folders). Patch by Serhiy Storchaka.

  • gh-83162: Renamed re.error to PatternError for clarity, and kept re.error for backward compatibility. Patch by Matthias Bussonnier and Adam Chhina.

  • gh-91133: Fix a bug in tempfile.TemporaryDirectory cleanup, which now no longer dereferences symlinks when working around file system permission errors.

  • bpo-43153: On Windows, tempfile.TemporaryDirectory previously masked a PermissionError with NotADirectoryError during directory cleanup. It now correctly raises PermissionError if errors are not ignored. Patch by Andrei Kulakov and Ken Jin.

  • bpo-32731: getpass.getuser() now raises OSError for all failures rather than ImportError on systems lacking the pwd module or KeyError if the password database is empty.

  • bpo-34321: mmap.mmap now has a trackfd parameter on Unix; if it is False, the file descriptor specified by fileno will not be duplicated.

  • bpo-35332: The shutil.rmtree() function now ignores errors when calling os.close() when ignore_errors is True, and os.close() no longer retried after error.

  • bpo-35928: io.TextIOWrapper now correctly handles the decoding buffer after read() and write().

  • bpo-26791: shutil.move() now moves a symlink into a directory when that directory is the target of the symlink. This provides the same behavior as the mv shell command. The previous behavior raised an exception. Patch by Jeffrey Kintscher.

  • bpo-41422: Fixed memory leaks of pickle.Pickler and pickle.Unpickler involving cyclic references via the internal memo mapping.

  • bpo-19821: The pydoc.ispackage() function has been deprecated.

  • bpo-40262: The ssl.SSLSocket.recv_into() method no longer requires the buffer argument to implement __len__ and supports buffers with arbitrary item size.

  • bpo-39912: warnings.filterwarnings() and warnings.simplefilter() now raise appropriate exceptions instead of AssertionError. Patch contributed by Rémi Lapeyre.

  • bpo-37260: Fixed a race condition in shutil.rmtree() in which directory entries removed by another process or thread while shutil.rmtree() is running can cause it to raise FileNotFoundError. Patch by Jeffrey Kintscher.

  • bpo-36959: Fix some error messages for invalid ISO format string combinations in strptime() that referred to directives not contained in the format string. Patch by Gordon P. Hemsley.

  • bpo-18060: Fixed a class inheritance issue that can cause segfaults when deriving two or more levels of subclasses from a base class of Structure or Union.

  • bpo-29779: Add a new PYTHON_HISTORY environment variable to set the location of a .python_history file.

  • bpo-21360: mailbox.Maildir now ignores files with a leading dot.

Documentation

  • gh-111699: Relocate smtpd deprecation notice to its own section rather than under locale in What’s New in Python 3.12 document

  • gh-110746: Improved markup for valid options/values for methods ttk.treeview.column and ttk.treeview.heading, and for Layouts.

  • gh-95649: Document that the asyncio module contains code taken from v0.16.0 of the uvloop project, as well as the required MIT licensing information.

Tests

  • gh-111798: Disable test_super_deep() from test_call under pydebug builds on WASI; the stack depth is too small to make the test useful.

  • gh-111801: Lower the recursion limit in test_isinstance for test_infinitely_many_bases(). This prevents a stack overflow on a pydebug build of WASI.

  • gh-111802: Specify a low recursion depth for test_bad_getattr() in test.pickletester to avoid exhausting the stack under a pydebug build for WASI.

  • gh-44626: Fix os.path.isabs() incorrectly returning True when given a path that starts with exactly one (back)slash on Windows.

    Fix pathlib.PureWindowsPath.is_absolute() incorrectly returning False for some paths beginning with two (back)slashes.

  • gh-113633: Use module state for the _testcapi extension module.

  • gh-109980: Fix test_tarfile_vs_tar in test_shutil for macOS, where system tar can include more information in the archive than shutil.make_archive.

  • gh-112769: The tests now correctly compare zlib version when zlib.ZLIB_RUNTIME_VERSION contains non-integer suffixes. For example zlib-ng defines the version as 1.3.0.zlib-ng.

  • gh-112334: Adds a regression test to verify that vfork() is used when expected by subprocess on vfork enabled POSIX systems (Linux).

  • gh-108927: Fixed order dependence in running tests in the same process when a test that has submodules (e.g. test_importlib) follows a test that imports its submodule (e.g. test_importlib.util) and precedes a test (e.g. test_unittest or test_compileall) that uses that submodule.

  • bpo-40648: Test modes that file can get with chmod() on Windows.

Build

  • gh-114013: Fix Tools/wasm/wasi.py to not include the path to python.wasm as part of HOSTRUNNER. The environment variable is meant to specify how to run the WASI host only, having python.wasm and relevant flags appended to the HOSTRUNNER. This fixes make test work.

  • gh-113258: Changed the Windows build to write out generated frozen modules into the build tree instead of the source tree.

  • gh-112305: Fixed the check-clean-src step performed on out of tree builds to detect errant $(srcdir)/Python/frozen_modules/*.h files and recommend appropriate source tree cleanup steps to get a working build again.

  • gh-112536: Add support for thread sanitizer (TSAN)

  • gh-112867: Fix the build for the case that WITH_PYMALLOC_RADIX_TREE=0 set.

  • gh-103065: Introduce Tools/wasm/wasi.py to simplify doing a WASI build.

  • bpo-11102: The os.major(), os.makedev(), and os.minor() functions are now available on HP-UX v3.

  • bpo-36351: Do not set ipv6type when cross-compiling.

Windows

  • gh-114096: Process privileges that are activated for creating directory junctions are now restored afterwards, avoiding behaviour changes in other parts of the program.

  • gh-111877: os.stat() calls were returning incorrect time values for files that could not be accessed directly.

  • gh-111973: Update Windows installer to use SQLite 3.44.2.

  • gh-113009: multiprocessing: On Windows, fix a race condition in Process.terminate(): no longer set the returncode attribute to always call WaitForSingleObject() in Process.wait(). Previously, sometimes the process was still running after TerminateProcess() even if GetExitCodeProcess() is not STILL_ACTIVE. Patch by Victor Stinner.

  • gh-86179: Fixes path calculations when launching Python on Windows through a symlink.

  • gh-71383: Update Tcl/Tk in Windows installer to 8.6.13 with a patch to suppress incorrect ThemeChanged warnings.

  • gh-111650: Ensures the Py_GIL_DISABLED preprocessor variable is defined in pyconfig.h so that extension modules written in C are able to use it.

  • gh-112278: Reduce the time cost for some functions in platform on Windows if current user has no permission to the WMI.

  • gh-73427: Deprecate sys._enablelegacywindowsfsencoding(). Use PYTHONLEGACYWINDOWSFSENCODING instead. Patch by Inada Naoki.

  • gh-87868: Correctly sort and remove duplicate environment variables in _winapi.CreateProcess().

  • bpo-37308: Fix mojibake in mmap.mmap when using a non-ASCII tagname argument on Windows.

macOS

  • gh-113666: Add the following constants to module stat: UF_SETTABLE, UF_TRACKED, UF_DATAVAULT, SF_SUPPORTED, SF_SETTABLE, SF_SYNTHETIC, SF_RESTRICTED, SF_FIRMLINK and SF_DATALESS. The values UF_SETTABLE, SF_SUPPORTED, SF_SETTABLE and SF_SYNTHETIC are only available on macOS.

  • gh-113536: os.waitid() is now available on macOS

  • gh-110459: Running configure ... --with-openssl-rpath=X/Y/Z no longer fails to detect OpenSSL on macOS.

  • gh-74573: Document that dbm.ndbm can silently corrupt DBM files on updates when exceeding undocumented platform limits, and can crash (segmentation fault) when reading such a corrupted file. (FB8919203)

  • gh-65701: The freeze tool doesn’t work with framework builds of Python. Document this and bail out early when running the tool with such a build.

  • gh-87277: webbrowser: Don’t look for X11 browsers on macOS. Those are generally not used and probing for them can result in starting XQuartz even if it isn’t used otherwise.

  • gh-111973: Update macOS installer to use SQLite 3.44.2.

  • gh-108269: Set CFBundleAllowMixedLocalizations to true in the Info.plist for the framework, embedded Python.app and IDLE.app with framework installs on macOS. This allows applications to pick up the user’s preferred locale when that’s different from english.

  • gh-102362: Make sure the result of sysconfig.get_plaform() includes at least a major and minor versions, even if MACOSX_DEPLOYMENT_TARGET is set to only a major version during build to match the format expected by pip.

  • gh-110017: Disable a signal handling stress test on macOS due to a bug in macOS (FB13453490).

  • gh-110820: Make sure the preprocessor definitions for ALIGNOF_MAX_ALIGN_T, SIZEOF_LONG_DOUBLE and HAVE_GCC_ASM_FOR_X64 are correct for Universal 2 builds on macOS.

  • gh-109981: Use /dev/fd on macOS to determine the number of open files in test.support.os_helper.fd_count to avoid a crash with “guarded” file descriptors when probing for open files.

IDLE

  • gh-72284: Improve the lists of features, editor key bindings, and shell key bingings in the IDLE doc.

  • gh-113903: Fix rare failure of test.test_idle, in test_configdialog.

  • gh-113729: Fix the “Help -> IDLE Doc” menu bug in 3.11.7 and 3.12.1.

  • gh-113269: Fix test_editor hang on macOS Catalina.

  • gh-112898: Fix processing unsaved files when quitting IDLE on macOS.

  • bpo-13586: Enter the selected text when opening the “Replace” dialog.

C API

Python 3.13.0 alpha 2

Release date: 2023-11-22

Core and Builtins

  • gh-112243: Don’t include comments in f-string debug expressions. Patch by Pablo Galindo

  • gh-112287: Slightly optimize the Tier 2 (uop) interpreter by only loading oparg and operand when needed. Also double the trace size limit again, to 512 this time.

  • gh-112266: Change docstrings of __dict__ and __weakref__.

  • gh-111807: Lower the max parser stack depth to 1000 under WASI debug builds.

  • gh-111798: When Python is built in debug mode, set the C recursion limit to 500 instead of 1500. A debug build is likely built with low optimization level which implies higher stack memory usage than a release build. Patch by Victor Stinner.

  • gh-106529: Enable translating unspecialized FOR_ITER to Tier 2.

  • gh-111916: Make hashlib related modules thread-safe without the GIL

  • gh-81137: Deprecate assignment to a function’s __code__ field when the new code object is of a mismatched type (e.g., from a generator to a plain function).

  • gh-79932: Raise exception if frame.clear() is called on a suspended frame.

  • gh-81925: Implement native thread ids for GNU KFreeBSD.

  • gh-111843: Use exponential backoff to reduce the number of failed tier 2 optimization attempts by over 99%.

  • gh-110829: Joining a thread now ensures the underlying OS thread has exited. This is required for safer fork() in multi-threaded processes.

  • gh-109369: Make sure that tier 2 traces are de-optimized if the code is instrumented

  • gh-111772: Specialize slot loads and stores for _Py_T_OBJECT as well as Py_T_OBJECT_EX

  • gh-111666: Speed up BaseExceptionGroup.derive(), BaseExceptionGroup.subgroup(), and BaseExceptionGroup.split() by changing how they parse passed arguments.

  • gh-111654: Fix runtime crash when some error happens in opcode LOAD_FROM_DICT_OR_DEREF.

  • gh-111623: Add support for sharing tuples between interpreters using the cross-interpreter API. Patch by Anthony Shaw.

  • gh-111354: The oparg of YIELD_VALUE is now 1 if the instruction is part of a yield-from or await, and 0 otherwise.

    The SUSPENDED frame state is now split into SUSPENDED and SUSPENDED_YIELD_FROM. This simplifies the code in _PyGen_yf.

  • gh-111520: Merge the Tier 1 (bytecode) and Tier 2 (micro-ops) interpreters together, moving the Tier 2 interpreter loop and switch into _PyEval_EvalFrameDefault() in Python/ceval.c. The Python/executor.c file is gone. Also the TIER_ONE and TIER_TWO macros are now handled by the code generator.

    Beware! This changes the environment variables to enable micro-ops and their debugging to PYTHON_UOPS and PYTHON_LLTRACE.

  • gh-109181: Speed up Traceback object creation by lazily compute the line number. Patch by Pablo Galindo

  • gh-111420: Allow type comments in parenthesized with statements

  • gh-111438: Add support for sharing floats between interpreters using the cross-interpreter API. Patch by Anthony Shaw.

  • gh-111435: Add support for sharing of True and False between interpreters using the cross-interpreter API. Patch by Anthony Shaw.

  • gh-102388: Fix a bug where iso2022_jp_3 and iso2022_jp_2004 codecs read out of bounds

  • gh-111366: Fix an issue in the codeop that was causing SyntaxError exceptions raised in the presence of invalid syntax to not contain precise error messages. Patch by Pablo Galindo

  • gh-111380: Fix a bug that was causing SyntaxWarning to appear twice when parsing if invalid syntax is encountered later. Patch by Pablo galindo

  • gh-111374: Added a new environment variable PYTHON_FROZEN_MODULES. It determines whether or not frozen modules are ignored by the import machinery, equivalent of the -X frozen_modules command-line option.

  • gh-111354: Remove oparg from YIELD_VALUE. Change oparg of RESUME to include information about the except-depth. These changes make it possible to simplify the code in generator close.

  • gh-94438: Fix a regression that prevented jumping across is None and is not None when debugging. Patch by Savannah Ostrowski.

  • gh-67224: Show source lines in tracebacks when using the -c option when running Python. Patch by Pablo Galindo

  • gh-111123: Fix a bug where a global declaration in an except block is rejected when the global is used in the else block.

  • gh-110938: Fix error messages for indented blocks with functions and classes with generic type parameters. Patch by Pablo Galindo

  • gh-109214: Remove unnecessary instruction pointer updates before returning from frames.

  • gh-110912: Correctly display the traceback for MemoryError exceptions using the traceback module. Patch by Pablo Galindo

  • gh-109894: Fixed crash due to improperly initialized static MemoryError in subinterpreter.

  • gh-110892: Return NULL for PyTrace_RETURN events caused by an exception

  • gh-110864: Fix argument parsing by _PyArg_UnpackKeywordsWithVararg for functions defining pos-or-keyword, vararg, and kw-only parameters.

  • gh-109094: Replace prev_instr on the interpreter frame by instr_ptr which points to the beginning of the instruction that is currently executing (or will execute once the frame resumes).

  • gh-110805: Allow the repl to show source code and complete tracebacks. Patch by Pablo Galindo

  • gh-110722: Add PYTHON_PRESITE=package.module to import a module early in the interpreter lifecycle before site.py is executed. Python needs to be built in debug mode for this option to exist.

  • gh-110481: Implement biased reference counting in --disable-gil builds.

  • gh-110543: Fix regression in Python 3.12 where types.CodeType.replace() would produce a broken code object if called on a module or class code object that contains a comprehension. Patch by Jelle Zijlstra.

  • gh-89519: Removed chained classmethod descriptors (introduced in bpo-19072). This can no longer be used to wrap other descriptors such as property. The core design of this feature was flawed and caused a number of downstream problems. To “pass-through” a classmethod, consider using the __wrapped__ attribute that was added in Python 3.10.

  • gh-103615: Use local events for opcode tracing

  • bpo-46657: Add mimalloc memory allocator support.

  • gh-106718: When PyConfig.stdlib_dir is explicitly set, it’s now respected and won’t be overridden by PyConfig.home.

  • gh-106905: Fix incorrect SystemError about AST constructor recursion depth mismatch.

  • gh-100445: Improve error message for unterminated strings with escapes.

  • bpo-45759: Improved error messages for elif/else statements not matching any valid statements. Patch by Jeremiah Vivian.

Library

Tests

  • gh-111808: Make the default value of test.support.infinite_recursion() to be conditional based on whether optimizations were used when compiling the interpreter. This helps with platforms like WASI whose stack size is greatly restricted in debug builds.

  • gh-110722: Gathering line coverage of standard libraries within the regression test suite is now precise, as well as much faster. Patch by Łukasz Langa.

  • gh-110367: Make regrtest --verbose3 option compatible with --huntrleaks -jN options. The ./python -m test -j1 -R 3:3 --verbose3 command now works as expected. Patch by Victor Stinner.

  • gh-111165: Remove no longer used functions run_unittest() and run_doctest() from the test.support module.

  • gh-110932: Fix regrtest if the SOURCE_DATE_EPOCH environment variable is defined: use the variable value as the random seed. Patch by Victor Stinner.

  • gh-110995: test_gdb: Fix detection of gdb built without Python scripting support. Patch by Victor Stinner.

  • gh-110918: Test case matching patterns specified by options --match, --ignore, --matchfile and --ignorefile are now tested in the order of specification, and the last match determines whether the test case be run or ignored.

  • gh-108747: Add unit test for usercustomize and sitecustomize hooks from site.

Build

  • gh-96954: Make make regen-unicodedata work for out-of-tree builds of CPython.

  • gh-112088: Add Tools/build/regen-configure.sh script to regenerate the configure with an Ubuntu container image. The quay.io/tiran/cpython_autoconf:271 container image (tiran/cpython_autoconf) is no longer used. Patch by Victor Stinner.

  • gh-111046: For wasi-threads, memory is now exported to fix compatibility issues with some wasm runtimes.

  • gh-110828: AIX 32bit needs -latomic to build the _testcapi extension module.

  • gh-85283: The errno, md5, resource, winsound, _ctypes_test, _multiprocessing.posixshmem, _scproxy, _stat, _testimportmultiple and _uuid C extensions are now built with the limited C API. Patch by Victor Stinner.

Windows

  • gh-111856: Fixes fstat() on file systems that do not support file ID requests. This includes FAT32 and exFAT.

  • gh-111293: Fix os.DirEntry.inode dropping higher 64 bits of a file id on some filesystems on Windows.

  • gh-110913: WindowsConsoleIO now correctly chunks large buffers without splitting up UTF-8 sequences.

macOS

  • gh-59703: For macOS framework builds, in getpath.c use the system dladdr function to find the path to the shared library rather than depending on deprecated macOS APIs.

  • gh-110950: Update macOS installer to include an upstream Tcl/Tk fix for the Secure coding is not enabled for restorable state! warning encountered in Tkinter on macOS 14 Sonoma.

  • gh-111015: Ensure that IDLE.app and Python Launcher.app are installed with appropriate permissions on macOS builds.

  • gh-71383: Update macOS installer to include an upstream Tcl/Tk fix for the ttk::ThemeChanged error encountered in Tkinter.

  • gh-92603: Update macOS installer to include a fix accepted by upstream Tcl/Tk for a crash encountered after the first tkinter.Tk() instance is destroyed.

IDLE

  • bpo-35668: Add docstrings to the IDLE debugger module. Fix two bugs: initialize Idb.botframe (should be in Bdb); in Idb.in_rpc_code, check whether prev_frame is None before trying to use it. Greatly expand test_debugger.

Tools/Demos

  • gh-111903: Argument Clinic now supports the @critical_section directive that instructs Argument Clinic to generate a critical section around the function call, which locks the self object in --disable-gil builds. Patch by Sam Gross.

C API

  • gh-112026: Add again the private _PyThreadState_UncheckedGet() function as an alias to the new public PyThreadState_GetUnchecked() function. Patch by Victor Stinner.

  • gh-112026: Restore the removed _PyDict_GetItemStringWithError() function. It is used by numpy. Patch by Victor Stinner.

  • gh-112026: Restore removed private C API functions, macros and structures which have no simple replacement for now:

    • _PyDict_GetItem_KnownHash()

    • _PyDict_NewPresized()

    • _PyHASH_BITS

    • _PyHASH_IMAG

    • _PyHASH_INF

    • _PyHASH_MODULUS

    • _PyHASH_MULTIPLIER

    • _PyLong_Copy()

    • _PyLong_FromDigits()

    • _PyLong_New()

    • _PyLong_Sign()

    • _PyObject_CallMethodId()

    • _PyObject_CallMethodNoArgs()

    • _PyObject_CallMethodOneArg()

    • _PyObject_CallOneArg()

    • _PyObject_EXTRA_INIT

    • _PyObject_FastCallDict()

    • _PyObject_GetAttrId()

    • _PyObject_Vectorcall()

    • _PyObject_VectorcallMethod()

    • _PyStack_AsDict()

    • _PyThread_CurrentFrames()

    • _PyUnicodeWriter structure

    • _PyUnicodeWriter_Dealloc()

    • _PyUnicodeWriter_Finish()

    • _PyUnicodeWriter_Init()

    • _PyUnicodeWriter_Prepare()

    • _PyUnicodeWriter_PrepareKind()

    • _PyUnicodeWriter_WriteASCIIString()

    • _PyUnicodeWriter_WriteChar()

    • _PyUnicodeWriter_WriteLatin1String()

    • _PyUnicodeWriter_WriteStr()

    • _PyUnicodeWriter_WriteSubstring()

    • _PyUnicode_AsString()

    • _PyUnicode_FromId()

    • _PyVectorcall_Function()

    • _Py_IDENTIFIER()

    • _Py_c_abs()

    • _Py_c_diff()

    • _Py_c_neg()

    • _Py_c_pow()

    • _Py_c_prod()

    • _Py_c_quot()

    • _Py_c_sum()

    • _Py_static_string()

    • _Py_static_string_init()

    Patch by Victor Stinner.

  • gh-112026: Add again <ctype.h> and <unistd.h> includes in Python.h, but don’t include them in the limited C API version 3.13 and newer. Patch by Victor Stinner.

  • gh-111956: Add internal-only one-time initialization API: _PyOnceFlag and _PyOnceFlag_CallOnce.

  • gh-111262: Add PyDict_Pop() and PyDict_PopString() functions: remove a key from a dictionary and optionally return the removed value. This is similar to dict.pop(), but without the default value and not raising KeyError if the key missing. Patch by Stefan Behnel and Victor Stinner.

  • gh-111863: Rename Py_NOGIL to Py_GIL_DISABLED. Patch by Hugo van Kemenade.

  • gh-111138: Add PyList_Extend() and PyList_Clear() functions: similar to Python list.extend() and list.clear() methods. Patch by Victor Stinner.

  • gh-108765: On Windows, Python.h no longer includes the <stddef.h> standard header file. If needed, it should now be included explicitly. Patch by Victor Stinner.

  • gh-111569: Implement “Python Critical Sections” from PEP 703. These are macros to help replace the GIL with per-object locks in the --disable-gil build of CPython. The macros are no-ops in the default build.

  • gh-111506: In the limited C API version 3.13, Py_SET_REFCNT() function is now implemented as an opaque function call. Patch by Victor Stinner.

  • gh-108082: Add PyErr_FormatUnraisable() function.

  • gh-110964: Move the undocumented private _PyArg functions and _PyArg_Parser structure to internal C API (pycore_modsupport.h). Patch by Victor Stinner.

  • gh-110815: Support non-ASCII keyword names in PyArg_ParseTupleAndKeywords().

  • gh-109587: Introduced PyUnstable_PerfTrampoline_CompileCode(), PyUnstable_PerfTrampoline_SetPersistAfterFork() and PyUnstable_CopyPerfMapFile(). These functions allow extension modules to initialize trampolines eagerly, after the application is “warmed up”. This makes it possible to have perf-trampolines running in an always-enabled fashion.

  • gh-85283: Add the PySys_Audit() function to the limited C API. Patch by Victor Stinner.

  • gh-85283: Add PyMem_RawMalloc(), PyMem_RawCalloc(), PyMem_RawRealloc() and PyMem_RawFree() to the limited C API. Patch by Victor Stinner.

  • gh-106672: Functions PyDict_GetItem(), PyDict_GetItemString(), PyMapping_HasKey(), PyMapping_HasKeyString(), PyObject_HasAttr(), PyObject_HasAttrString(), and PySys_GetObject(), which clear all errors occurred during calling the function, report now them using sys.unraisablehook().

  • gh-67565: Remove redundant C-contiguity check in getargs.c, binascii, ssl and Argument Clinic. Patched by Stefan Krah and Furkan Onder

Python 3.13.0 alpha 1

Release date: 2023-10-13

Security

  • gh-108310: Fixed an issue where instances of ssl.SSLSocket were vulnerable to a bypass of the TLS handshake and included protections (like certificate verification) and treating sent unencrypted data as if it were post-handshake TLS encrypted data. Security issue reported as CVE 2023-40217 by Aapo Oksman. Patch by Gregory P. Smith.

  • gh-107774: PEP 669 specifies that sys.monitoring.register_callback will generate an audit event. Pre-releases of Python 3.12 did not generate the audit event. This is now fixed.

  • gh-102988: Reverted the email.utils security improvement change released in 3.12beta4 that unintentionally caused email.utils.getaddresses to fail to parse email addresses with a comma in the quoted name field. See gh-106669.

  • gh-99108: Refresh our new HACL* built-in hashlib code from upstream. Built-in SHA2 should be faster and an issue with SHA3 on 32-bit platforms is fixed.

  • gh-102509: Start initializing ob_digit during creation of PyLongObject objects. Patch by Illia Volochii.

Core and Builtins

  • gh-110782: Fix crash when typing.TypeVar is constructed with a keyword argument. Patch by Jelle Zijlstra.

  • gh-110752: Reset ceval.eval_breaker in interpreter_clear()

  • gh-110721: Use the traceback implementation for the default PyErr_Display() functionality. Patch by Pablo Galindo

  • gh-110696: Fix incorrect error message for invalid argument unpacking. Patch by Pablo Galindo

  • gh-104169: Split the tokenizer into two separate directories: - One part includes the actual lexeme producing logic and lives in Parser/lexer. - The second part wraps the lexer according to the different tokenization modes we have (string, utf-8, file, interactive, readline) and lives in Parser/tokenizer.

  • gh-110688: Remove undocumented test_c_api method from set, which was only defined for testing purposes under Py_DEBUG. Now we have proper CAPI tests.

  • gh-104584: Fix a reference leak when running with PYTHONUOPS or -X uops enabled.

  • gh-110514: Add PY_THROW to sys.setprofile() events

  • gh-110489: Optimise math.ceil() when the input is exactly a float, resulting in about a 10% improvement.

  • gh-110455: Guard assert(tstate->thread_id > 0) with #ifndef HAVE_PTHREAD_STUBS. This allows for for pydebug builds to work under WASI which (currently) lacks thread support.

  • gh-110309: Remove unnecessary empty constant nodes in the ast of f-string specs.

  • gh-110259: Correctly identify the format spec in f-strings (with single or triple quotes) that have multiple lines in the expression part and include a formatting spec. Patch by Pablo Galindo

  • gh-110237: Fix missing error checks for calls to PyList_Append in _PyEval_MatchClass.

  • gh-110164: regrtest: If the SOURCE_DATE_EPOCH environment variable is defined, regrtest now disables tests randomization. Patch by Victor Stinner.

  • gh-109889: Fix the compiler’s redundant NOP detection algorithm to skip over NOPs with no line number when looking for the next instruction’s lineno.

  • gh-109853: sys.path[0] is now set correctly for subinterpreters.

  • gh-109923: Set line number on the POP_TOP that follows a RETURN_GENERATOR.

  • gh-105716: Subinterpreters now correctly handle the case where they have threads running in the background. Before, such threads would interfere with cleaning up and destroying them, as well as prevent running another script.

  • gh-109369: The internal eval_breaker and supporting flags, plus the monitoring version have been merged into a single atomic integer to speed up checks.

  • gh-109823: Fix bug where compiler does not adjust labels when removing an empty basic block which is a jump target.

  • gh-109793: The main thread no longer exits prematurely when a subinterpreter is cleaned up during runtime finalization. The bug was a problem particularly because, when triggered, the Python process would always return with a 0 exitcode, even if it failed.

  • gh-109719: Fix missing jump target labels when compiler reorders cold/warm blocks.

  • gh-109595: Add -X cpu_count command line option to override return results of os.cpu_count() and os.process_cpu_count(). This option is useful for users who need to limit CPU resources of a container system without having to modify the container (application code). Patch by Donghee Na.

  • gh-109627: Fix bug where the compiler does not assign a new jump target label to a duplicated small exit block.

  • gh-109596: Fix some tokens in the grammar that were incorrectly marked as soft keywords. Also fix some repeated rule names and ensure that repeated rules are not allowed. Patch by Pablo Galindo

  • gh-109496: On a Python built in debug mode, Py_DECREF() now calls _Py_NegativeRefcount() if the object is a dangling pointer to deallocated memory: memory filled with 0xDD “dead byte” by the debug hook on memory allocators. The fix is to check the reference count before checking for _Py_IsImmortal(). Patch by Victor Stinner.

  • gh-107265: Deopt opcodes hidden by the executor when base opcode is needed

  • gh-109371: Deopted instructions correctly for tool initialization and modified the incorrect assertion in instrumentation, when a previous tool already sets INSTRUCTION events

  • gh-105658: Fix bug where the line trace of an except block ending with a conditional includes an excess event with the line of the conditional expression.

  • gh-109219: Fix compiling type param scopes that use a name which is also free in an inner scope.

  • gh-109351: Fix crash when compiling an invalid AST involving a named (walrus) expression.

  • gh-109341: Fix crash when compiling an invalid AST involving a ast.TypeAlias.

  • gh-109195: Fix source location for the LOAD_* instruction preceding a LOAD_SUPER_ATTR to load the super global (or shadowing variable) so that it encompasses only the name super and not the following parentheses.

  • gh-109256: Opcode IDs for specialized opcodes are allocated in their own range to improve stability of the IDs for the ‘real’ opcodes.

  • gh-109216: Fix possible memory leak in BUILD_MAP.

  • gh-109207: Fix a SystemError in __repr__ of symtable entry object.

  • gh-109179: Fix bug where the C traceback display drops notes from SyntaxError.

  • gh-109118: Disallow nested scopes (lambdas, generator expressions, and comprehensions) within PEP 695 annotation scopes that are nested within classes.

  • gh-109156: Add tests for de-instrumenting instructions while keeping the instrumentation for lines

  • gh-109114: Relax the detection of the error message for invalid lambdas inside f-strings to not search for arbitrary replacement fields to avoid false positives. Patch by Pablo Galindo

  • gh-105848: Add a new CALL_KW opcode, used for calls containing keyword arguments. Also, fix a possible crash when jumping over method calls in a debugger.

  • gh-109052: Use the base opcode when comparing code objects to avoid interference from instrumentation

  • gh-109118: Fix interpreter crash when a NameError is raised inside the type parameters of a generic class.

  • gh-88943: Improve syntax error for non-ASCII character that follows a numerical literal. It now points on the invalid non-ASCII character, not on the valid numerical literal.

  • gh-108976: Fix crash that occurs after de-instrumenting a code object in a monitoring callback.

  • gh-108732: Make iteration variables of module- and class-scoped comprehensions visible to pdb and other tools that use frame.f_locals again.

  • gh-108959: Fix caret placement for error locations for subscript and binary operations that involve non-semantic parentheses and spaces. Patch by Pablo Galindo

  • gh-104584: Fix a crash when running with PYTHONUOPS or -X uops enabled and an error occurs during optimization.

  • gh-108727: Define tp_dealloc for CounterOptimizer_Type. This fixes a segfault on deallocation.

  • gh-108520: Fix multiprocessing.synchronize.SemLock.__setstate__() to properly initialize multiprocessing.synchronize.SemLock._is_fork_ctx. This fixes a regression when passing a SemLock across nested processes.

    Rename multiprocessing.synchronize.SemLock.is_fork_ctx to multiprocessing.synchronize.SemLock._is_fork_ctx to avoid exposing it as public API.

  • gh-108654: Restore locals shadowed by an inlined comprehension if the comprehension raises an exception.

  • gh-108488: Change the initialization of inline cache entries so that the cache entry for JUMP_BACKWARD is initialized to zero, instead of the adaptive_counter_warmup() value used for all other instructions. This counter, unique among instructions, counts up from zero.

  • gh-108716: Turn off deep-freezing of code objects. Modules are still frozen, so that a file system search is not needed for common modules.

  • gh-108614: Add RESUME_CHECK instruction, to avoid having to handle instrumentation, signals, and contexts switches in the tier 2 execution engine.

  • gh-108487: Move an assert that would cause a spurious crash in a devious case that should only trigger deoptimization.

  • gh-106176: Use a WeakValueDictionary to track the lists containing the modules each thread is currently importing. This helps avoid a reference leak from keeping the list around longer than necessary. Weakrefs are used as GC can’t interrupt the cleanup.

  • gh-105481: The regen-opcode build stage was removed and its work is now done in regen-cases.

  • gh-107901: Fix missing line number on JUMP_BACKWARD at the end of a for loop.

  • gh-108113: The compile() built-in can now accept a new flag, ast.PyCF_OPTIMIZED_AST, which is similar to ast.PyCF_ONLY_AST except that the returned AST is optimized according to the value of the optimize argument.

    ast.parse() now accepts an optional argument optimize which is passed on to the compile() built-in. This makes it possible to obtain an optimized AST.

  • gh-107971: Opcode IDs are generated from bytecodes.c instead of being hard coded in opcode.py.

  • gh-107944: Improve error message for function calls with bad keyword arguments. Patch by Pablo Galindo

  • gh-108390: Raise an exception when setting a non-local event (RAISE, EXCEPTION_HANDLED, etc.) in sys.monitoring.set_local_events.

    Fixes crash when tracing in recursive calls to Python classes.

  • gh-108035: Remove the _PyCFrame struct, moving the pointer to the current interpreter frame back to the threadstate, as it was for 3.10 and earlier. The _PyCFrame existed as a performance optimization for tracing. Since PEP 669 has been implemented, this optimization no longer applies.

  • gh-91051: Fix abort / segfault when using all eight type watcher slots, on platforms where char is signed by default.

  • gh-106581: Fix possible assertion failures and missing instrumentation events when PYTHONUOPS or -X uops is enabled.

  • gh-107526: Revert converting vars, dir, next, getattr, and iter to argument clinic.

  • gh-84805: Autogenerate signature for METH_NOARGS and METH_O extension functions.

  • gh-107758: Make the dump_stack() routine used by the lltrace feature (low-level interpreter debugging) robust against recursion by ensuring that it never calls a __repr__ method implemented in Python. Also make the similar output for Tier-2 uops appear on stdout (instead of stderr), to match the lltrace code in ceval.c.

  • gh-107659: Add docstrings for ctypes.pointer() and ctypes.POINTER().

  • gh-105848: Modify the bytecode so that the actual callable for a CALL is at a consistent position on the stack (regardless of whether or not bound-method-calling optimizations are active).

  • gh-107674: Fixed performance regression in sys.settrace.

  • gh-107724: In pre-release versions of 3.12, up to rc1, the sys.monitoring callback function for the PY_THROW event was missing the third, exception argument. That is now fixed.

  • gh-84436: Skip reference count modifications for many known immortal objects.

  • gh-107596: Specialize subscripting str objects by int indexes.

  • gh-107080: Trace refs builds (--with-trace-refs) were crashing when used with isolated subinterpreters. The problematic global state has been isolated to each interpreter. Other fixing the crashes, this change does not affect users.

  • gh-107557: Generate the cases needed for the barebones tier 2 abstract interpreter for optimization passes in CPython.

  • gh-106608: Make _PyUOpExecutorObject variable length.

  • gh-100964: Clear generators’ exception state after return to break reference cycles.

  • gh-107455: Improve error messages when converting an incompatible type to ctypes.c_char_p, ctypes.c_wchar_p and ctypes.c_void_p.

  • gh-107263: Increase C recursion limit for functions other than the main interpreter from 800 to 1500. This should allow functions like list.__repr__ and json.dumps to handle all the inputs that they could prior to 3.12

  • gh-104584: Fix an issue which caused incorrect inline caches to be read when running with PYTHONUOPS or -X uops enabled.

  • gh-104432: Fix potential unaligned memory access on C APIs involving returned sequences of char * pointers within the grp and socket modules. These were revealed using a -fsaniziter=alignment build on ARM macOS. Patch by Christopher Chavez.

  • gh-106078: Isolate _decimal (apply PEP 687). Patch by Charlie Zhao.

  • gh-106898: Add the exception as the third argument to PY_UNIND callbacks in sys.monitoring. This makes the PY_UNWIND callback consistent with the other exception handling callbacks.

  • gh-106895: Raise a ValueError when a monitoring callback function returns DISABLE for events that cannot be disabled locally.

  • gh-106897: Add a RERAISE event to sys.monitoring, which occurs when an exception is reraise, either explicitly by a plain raise statement, or implicitly in an except or finally block.

  • gh-77377: Ensure that multiprocessing synchronization objects created in a fork context are not sent to a different process created in a spawn context. This changes a segfault into an actionable RuntimeError in the parent process.

  • gh-106931: Statically allocated string objects are now interned globally instead of per-interpreter. This fixes a situation where such a string would only be interned in a single interpreter. Normal string objects are unaffected.

  • gh-104621: Unsupported modules now always fail to be imported.

  • gh-107122: Add dbm.ndbm.ndbm.clear() to dbm.ndbm. Patch By Donghee Na.

  • gh-107122: Add dbm.gnu.gdbm.clear() to dbm.gnu. Patch By Donghee Na.

  • gh-107015: The ASYNC and AWAIT tokens are removed from the Grammar, which removes the possibility of making async and await soft keywords when using feature_version<7 in ast.parse().

  • gh-106917: Fix classmethod-style super() method calls (i.e., where the second argument to super(), or the implied second argument drawn from self/cls in the case of zero-arg super, is a type) when the target of the call is not a classmethod.

  • gh-105699: Python no longer crashes due an infrequent race when initializing per-interpreter interned strings. The crash would manifest when the interpreter was finalized.

  • gh-105699: Python no longer crashes due to an infrequent race in setting Py_FileSystemDefaultEncoding and Py_FileSystemDefaultEncodeErrors (both deprecated), when simultaneously initializing two isolated subinterpreters. Now they are only set during runtime initialization.

  • gh-106908: Fix various hangs, reference leaks, test failures, and tracing/introspection bugs when running with PYTHONUOPS or -X uops enabled.

  • gh-106092: Fix a segmentation fault caused by a use-after-free bug in frame_dealloc when the trashcan delays the deallocation of a PyFrameObject.

  • gh-106485: Reduce the number of materialized instances dictionaries by dematerializing them when possible.

  • gh-106719: No longer suppress arbitrary errors in the __annotations__ getter and setter in the type and module types.

  • gh-106723: Propagate frozen_modules to multiprocessing spawned process interpreters.

  • gh-104909: Split LOAD_ATTR_INSTANCE_VALUE into micro-ops.

  • gh-104909: Split LOAD_GLOBAL specializations into micro-ops.

  • gh-106597: A new debug structure of offsets has been added to the _PyRuntimeState that will help out-of-process debuggers and profilers to obtain the offsets to relevant interpreter structures in a way that is agnostic of how Python was compiled and that doesn’t require copying the headers. Patch by Pablo Galindo

  • gh-106487: Allow the count argument of str.replace() to be a keyword. Patch by Hugo van Kemenade.

  • gh-96844: Improve error message of list.remove(). Patch by Donghee Na.

  • gh-81283: Compiler now strips indents from docstrings. It reduces pyc file size 5% when the module is heavily documented. This change affects to __doc__ so tools like doctest will be affected.

  • gh-106396: When the format specification of an f-string expression is empty, the parser now generates an empty ast.JoinedStr node for it instead of an one-element ast.JoinedStr with an empty string ast.Constant.

  • gh-100288: Specialize LOAD_ATTR for non-descriptors on the class. Adds LOAD_ATTR_NONDESCRIPTOR_WITH_VALUES and LOAD_ATTR_NONDESCRIPTOR_NO_DICT.

  • gh-106008: Fix possible reference leaks when failing to optimize comparisons with None in the bytecode compiler.

  • gh-106145: Make end_lineno and end_col_offset required on type_param ast nodes.

  • gh-106213: Changed the way that Emscripten call trampolines work for compatibility with Wasm/JS Promise integration.

  • gh-106182: sys.getfilesystemencoding() and sys.getfilesystemencodeerrors now return interned Unicode object.

  • gh-106210: Removed Emscripten import trampoline as it was no longer necessary for Pyodide.

  • gh-104584: Added a new, experimental, tracing optimizer and interpreter (a.k.a. “tier 2”). This currently pessimizes, so don’t use yet – this is infrastructure so we can experiment with optimizing passes. To enable it, pass -Xuops or set PYTHONUOPS=1. To get debug output, set PYTHONUOPSDEBUG=N where N is a debug level (0-4, where 0 is no debug output and 4 is excessively verbose).

  • gh-105775: LOAD_CLOSURE is now a pseudo-op.

  • gh-105730: Allow any callable other than type objects as the condition predicate in BaseExceptionGroup.split() and BaseExceptionGroup.subgroup().

  • gh-105979: Fix crash in _imp.get_frozen_object() due to improper exception handling.

  • gh-106003: Add a new TO_BOOL instruction, which performs boolean conversions for POP_JUMP_IF_TRUE, POP_JUMP_IF_FALSE, and UNARY_NOT (which all expect exact bool values now). Also, modify the oparg of COMPARE_OP to include an optional “boolean conversion” flag.

  • gh-98931: Ensure custom SyntaxError error messages are raised for invalid imports with multiple targets. Patch by Pablo Galindo

  • gh-105724: Improve assert error messages by providing exact error range.

  • gh-105908: Fixed bug where gh-99111 breaks future import barry_as_FLUFL in the Python REPL.

  • gh-105840: Fix possible crashes when specializing function calls with too many __defaults__.

  • gh-105831: Fix an f-string bug, where using a debug expression (the = sign) that appears in the last line of a file results to the debug buffer that holds the expression text being one character too small.

  • gh-105800: Correctly issue SyntaxWarning in f-strings if invalid sequences are used. Patch by Pablo Galindo

  • gh-105340: Include the comprehension iteration variable in locals() inside a module- or class-scope comprehension.

  • gh-105331: Raise ValueError if the delay argument to asyncio.sleep() is a NaN (matching time.sleep()).

  • gh-105587: The runtime can’t guarantee that immortal objects will not be mutated by Extensions. Thus, this modifies _PyStaticObject_CheckRefcnt to warn instead of asserting.

  • gh-105564: Don’t include artificil newlines in the line attribute of tokens in the APIs of the tokenize module. Patch by Pablo Galindo

  • gh-105549: Tokenize separately NUMBER and NAME tokens that are not ambiguous. Patch by Pablo Galindo.

  • gh-105588: Fix an issue that could result in crashes when compiling malformed ast nodes.

  • gh-100987: Allow objects other than code objects as the “executable” in internal frames. In the long term, this can help tools like Cython and PySpy interact more efficiently. In the shorter term, it allows us to perform some optimizations more simply.

  • gh-105375: Fix bugs in the builtins module where exceptions could end up being overwritten.

  • gh-105375: Fix bug in the compiler where an exception could end up being overwritten.

  • gh-105375: Improve error handling in PyUnicode_BuildEncodingMap() where an exception could end up being overwritten.

  • gh-105486: Change the repr of ParamSpec list of args in types.GenericAlias.

  • gh-105678: Break the MAKE_FUNCTION instruction into two parts, MAKE_FUNCTION which makes the function and SET_FUNCTION_ATTRIBUTE which sets the attributes on the function. This makes the stack effect of MAKE_FUNCTION regular to ease optimization and code generation.

  • gh-105435: Fix spurious newline character if file ends on a comment without a newline. Patch by Pablo Galindo

  • gh-105390: Correctly raise tokenize.TokenError exceptions instead of SyntaxError for tokenize errors such as incomplete input. Patch by Pablo Galindo

  • gh-105259: Don’t include newline character for trailing NEWLINE tokens emitted in the tokenize module. Patch by Pablo Galindo

  • gh-104635: Eliminate redundant STORE_FAST instructions in the compiler. Patch by Donghee Na and Carl Meyer.

  • gh-105324: Fix the main function of the tokenize module when reading from sys.stdin. Patch by Pablo Galindo

  • gh-33092: Simplify and speed up interpreter for f-strings. Removes FORMAT_VALUE opcode. Add CONVERT_VALUE, FORMAT_SIMPLE and FORMAT_WITH_SPEC opcode. Compiler emits more efficient sequence for each format expression.

  • gh-105229: Remove remaining two-codeunit superinstructions. All remaining superinstructions only take a single codeunit, simplifying instrumentation and quickening.

  • gh-105235: Prevent out-of-bounds memory access during mmap.find() calls.

  • gh-98963: Restore the ability for a subclass of property to define __slots__ or otherwise be dict-less by ignoring failures to set a docstring on such a class. This behavior had regressed in 3.12beta1. An AttributeError where there had not previously been one was disruptive to existing code.

  • gh-104812: The “pending call” machinery now works for all interpreters, not just the main interpreter, and runs in all threads, not just the main thread. Some calls are still only done in the main thread, ergo in the main interpreter. This change does not affect signal handling nor the existing public C-API (Py_AddPendingCall()), which both still only target the main thread. The new functionality is meant strictly for internal use for now, since consequences of its use are not well understood yet outside some very restricted cases. This change brings the capability in line with the intention when the state was made per-interpreter several years ago.

  • gh-105194: Do not escape with backslashes f-string format specifiers. Patch by Pablo Galindo

  • gh-105229: Replace some dynamic superinstructions with single instruction equivalents.

  • gh-105162: Fixed bug in generator.close()/throw() where an inner iterator would be ignored when the outer iterator was instrumented.

  • gh-105164: Ensure annotations are set up correctly if the only annotation in a block is within a match block. Patch by Jelle Zijlstra.

  • gh-105148: Make _PyASTOptimizeState internal to ast_opt.c. Make _PyAST_Optimize take two integers instead of a pointer to this struct. This avoids the need to include pycore_compile.h in ast_opt.c.

  • gh-104799: Attributes of ast nodes that are lists now default to the empty list if omitted. This means that some code that previously raised TypeError when the AST node was used will now proceed with the empty list instead. Patch by Jelle Zijlstra.

  • gh-105111: Remove the old trashcan macros Py_TRASHCAN_SAFE_BEGIN and Py_TRASHCAN_SAFE_END. They should be replaced by the new macros Py_TRASHCAN_BEGIN and Py_TRASHCAN_END.

  • gh-105035: Fix super() calls on types with custom tp_getattro implementation (e.g. meta-types.)

  • gh-105017: Show CRLF lines in the tokenize string attribute in both NL and NEWLINE tokens. Patch by Marta Gómez.

  • gh-105013: Fix handling of multiline parenthesized lambdas in inspect.getsource(). Patch by Pablo Galindo

  • gh-105017: Do not include an additional final NL token when parsing files having CRLF lines. Patch by Marta Gómez.

  • gh-104976: Ensure that trailing DEDENT tokenize.TokenInfo objects emitted by the tokenize module are reported as in Python 3.11. Patch by Pablo Galindo

  • gh-104972: Ensure that the line attribute in tokenize.TokenInfo objects in the tokenize module are always correct. Patch by Pablo Galindo

  • gh-104955: Fix signature for the new __release_buffer__() slot. Patch by Jelle Zijlstra.

  • gh-104690: Starting new threads and process creation through os.fork() during interpreter shutdown (such as from atexit handlers) is no longer supported. It can lead to race condition between the main Python runtime thread freeing thread states while internal threading routines are trying to allocate and use the state of just created threads. Or forked children trying to use the mid-shutdown runtime and thread state in the child process.

  • gh-104879: Fix crash when accessing the __module__ attribute of type aliases defined outside a module. Patch by Jelle Zijlstra.

  • gh-104825: Tokens emitted by the tokenize module do not include an implicit \n character in the line attribute anymore. Patch by Pablo Galindo

  • gh-104770: If a generator returns a value upon being closed, the value is now returned by generator.close().

  • gh-89091: Raise RuntimeWarning for unawaited async generator methods like asend(), athrow() and aclose(). Patch by Kumar Aditya.

  • gh-96663: Add a better, more introspect-able error message when setting attributes on classes without a __dict__ and no slot member for the attribute.

  • gh-93627: Update the Python pickle module implementation to match the C implementation of the pickle module. For objects setting reduction methods like __reduce_ex__() or __reduce__() to