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Segmentation fault after deleting __fields__ attribute from ast.AST #126105

Description

@federicovalenso

Crash report

What happened?

>>> import ast
>>> dir(ast.AST)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__match_args__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_attributes', '_fields']
>>> del ast.AST._fields
>>> dir(ast.AST)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__match_args__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_attributes']
>>> t = ast.AST(arg1=123)
Segmentation fault

This happens because fields variable is null-pointer here, moreover it was previously checked for null here.

CPython versions tested on:

3.11

Operating systems tested on:

Linux

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

Python 3.11.9 (main, Oct 28 2024, 23:26:29) [GCC 13.2.0]

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3.12only security fixes3.13only security fixes3.14bugs and security fixesinterpreter-core(Objects, Python, Grammar, and Parser dirs)type-crashA hard crash of the interpreter, possibly with a core dump

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