Feature or enhancement

Proposal:

We can improve performance of cpython by using stealing methods (_PyList_AppendTakeRef, _PyDict_SetItem_Take2, PyTuple_FromPairSteal etc.) instead of the normal ones. Using stealing methods we typically avoid an incref/decref pair and sometimes error handling is simplified. We should only make changes where it makes a performance impact, the code is not more complex and the modules or methods affected are performance critical.

A list of possible cases (there might be more). The issue is open for anyone to work on.

Location	Module / context	Helper
Modules/_csv.c:688	csv reader, per field	_PyList_AppendTakeRef
Modules/pyexpat.c:472	pyexpat StartElement, per attribute	_PyDict_SetItem_Take2
Modules/_elementtree.c:3351	ElementTree C accel attrib dict	_PyDict_SetItem_Take2
Modules/_io/bytesio.c:577	io.BytesIO.readlines	_PyList_AppendTakeRef
Modules/_io/iobase.c:756	io.IOBase.readlines (generic)	_PyList_AppendTakeRef
Objects/frameobject.c:639 & 658	frame f_locals / vars() / tracing	_PyList_AppendTakeRef
Modules/_pickle.c:5138	pickle Pickler memo copy	_PyDict_SetItem_Take2
Modules/_io/textio.c:2337 & 2343	io.TextIOWrapper readline (multi-chunk)	_PyList_AppendTakeRef
Modules/_asynciomodule.c:1213	asyncio future done-callback compaction	_PyList_AppendTakeRef

Linked PRs

• gh-150942: Speed up re.findall and re.sub/subn result building #150943
• gh-150942: Speed up json.loads array and object decoding #150945
• gh-150942: Speed up csv.reader row building #150995
• gh-150942: Speed up frame local item collection #151002
• gh-151059: Use PyObject_CallMethodOneArg in datetime call_tzinfo_method #151062
• gh-150942: Speed up ElementTree attribute parsing #151209
• gh-150942: Optimize PicklerMemoProxy.copy() with _PyDict_SetItem_Take2 #151608
• gh-150942: Speed up asyncio Future.remove_done_callback #153013
• gh-150942: Speed up pyexpat attribute parsing #154860
• gh-150942: Speed up BytesIO.readlines() using reference-stealing append #155171
• gh-150942: Speed up IOBase.readlines #155304
• gh-150942: Optimize stringlib split/splitlines with _PyList_AppendTakeRef #155922
• gh-150942: Speed up re.split result building #155940
• gh-150942: Improve performance of csv reader by using _PyList_AppendT… #155957