Crash report

What happened?

In CPython 3.14 and later, assigning to the global __conditional_annotations__ before a variable annotation produces a segfault.

Here is a minimal reproducible example:

__conditional_annotations__ = 0
a: 1

Analyzing the bytecode, the compiler first initializes __conditional_annotations__ to an empty set. Whenever an annotation is declared, a SET_ADD is emitted under the assumption that the underlying type is still a set. But we can re-assign __conditional_annotations__ to another object in between, leading to a type confusion:

BUILD_SET                0
STORE_NAME               0 (__conditional_annotations__)
LOAD_SMALL_INT           0
STORE_NAME               0 (__conditional_annotations__)
LOAD_NAME                0 (__conditional_annotations__)
LOAD_SMALL_INT           0
SET_ADD                  1

CPython versions tested on:

3.14, 3.15

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

No response

Linked PRs

• gh-154902: Add an intrinsic for conditional annotations #155026
• [3.15] gh-154902: Type-check the SET_ADD operand #155071
• [3.14] gh-154902: Type-check the SET_ADD operand #155072