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gh-116021: Deprecate support for instantiating abstract AST nodes #137865

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gh-116021: Deprecate support for instantiating abstract AST nodes #137865

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@brianschubert brianschubert commented Aug 16, 2025 •
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Demonstration:

>>> ast.stmt()
<python-input-1>:1: DeprecationWarning: Instantiating abstract AST node class ast.stmt is deprecated. This will become an error in Python 3.20
stmt()

>>> class MyStmt(ast.stmt): pass
... 
>>> MyStmt()
MyStmt()

This uses an internal registry to track which nodes are abstract. Since the check for abstract-ness depends on the exact node type, this shouldn't affect user-defined subclasses of the abstract nodes.

📚 Documentation preview 📚: https://cpython-previews--137865.org.readthedocs.build/

@bedevere-app bedevere-app bot mentioned this pull request Aug 16, 2025
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brianschubert commented Aug 16, 2025
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Lib/test/test_sys.py
Comment on lines -1880 to +1881
check(_ast.AST(), size('P'))
with self.assertWarns(DeprecationWarning):
check(_ast.AST(), size('P'))
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I think this should probably be rewritten, but I'm not sure I understand the goal of this test well enough to do that

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