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GeezerVison is showing github.com — gh-116021: Deprecate support for instantiating abstract AST nodes by brianschubert · Pull Request #137865 · python/cpython

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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 tracks which AST nodes are abstract using an internal set that gets built during node type initialization. I tried a few different approaches, and this seemed the simplest. A nice thing about this approach is that the check for abstract-ness depends on the exact node type, so this avoids most inheritance subtleties that could interfere with existing user-defined subclasses.

Issue: Deprecate creation of abstract AST nodes #116021

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

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          Deprecate support for instantiating abstract AST nodes

1b767fc

brianschubert requested review from AA-Turner, Eclips4, JelleZijlstra, ericsnowcurrently, isidentical and tomasr8 as code owners

August 16, 2025 17:39

bedevere-app Bot added the awaiting review label

Aug 16, 2025

bedevere-app Bot mentioned this pull request

Aug 16, 2025

Deprecate creation of abstract AST nodes #116021

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brianschubert added 2 commits

August 16, 2025 13:52


          Missing static

b72a362


          Capture warning in test_sys

c8dda97

brianschubert commented

Aug 16, 2025

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Lib/test/test_sys.py Outdated

Comment on lines +1880 to +1881

		check(_ast.AST(), size('P'))
		with self.assertWarns(DeprecationWarning):
		check(_ast.AST(), size('P'))

brianschubert Aug 16, 2025 •

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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. Suggestions welcome!

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picnixz Aug 18, 2025

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It's to check that objects in Python/ have the correct types. I don't know why it's actually in test_sys though. I think we should split this test and move each check to the module it belongs (ast.AST's size should be checked in test_ast).

For now, leave it here. A separate issue should be opened.

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JelleZijlstra Oct 20, 2025

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I think it's here because it's arguably testing sys.getsizeof. Maybe it could be changed to test a concrete AST class instead?

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brianschubert Oct 27, 2025

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check(_ast.Module(), size('3P')) might work then? (not sure if I'm counting the object size right)

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brianschubert Nov 29, 2025

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@JelleZijlstra @picnixz any further thoughts re: above? Happy to update this is someone can confirm a good substitute

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JelleZijlstra Dec 2, 2025

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Yes, what you suggest should work (haven't verified the object size is right).

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brianschubert Feb 22, 2026

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Looking again 3P seems right, updated!

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picnixz reviewed

Aug 18, 2025

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Would it be easier to have a module function checking if a node is abstract? say _ast.is_abstract(node) (in the C module, not the Python module). That way we don't need an additional method on AST objects (which could be shadowed).

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Lib/test/test_sys.py Outdated

Comment on lines +1880 to +1881

		check(_ast.AST(), size('P'))
		with self.assertWarns(DeprecationWarning):
		check(_ast.AST(), size('P'))

picnixz Aug 18, 2025

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For now, leave it here. A separate issue should be opened.

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Parser/asdl_c.py Resolved

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Parser/asdl_c.py Outdated

		return result;
		}

		/* Helper for checking if a node class is abstract in the tests. */

picnixz Aug 18, 2025

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I think we should use clinic here, but this would create a new file as we don't use it at all. Maybe we can do it in a follow-up PR though.

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Lib/test/test_ast/test_ast.py Resolved

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brianschubert and others added 3 commits

August 18, 2025 17:06


          Convert _is_abstract to module function, address misc review comments

e550c2a

Co-authored-by: Bénédikt Tran <[email protected]>


          Retarget removal for Python 3.19

90b7428

3.14 + 5 = 3.19


          Add pending-removal-in-3.19.rst mention

16db374

brianschubert requested review from lysnikolaou and pablogsal as code owners

September 8, 2025 21:29

brianschubert added 3 commits

September 14, 2025 19:27


          Merge branch 'main' into pythongh-116021-ast-depr-abstract

2f390c8


          Merge branch 'main' into pythongh-116021-ast-depr-abstract

97dbdab


          Retarget removal for Python 3.20

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JelleZijlstra approved these changes

Oct 20, 2025

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Lib/test/test_sys.py Outdated

Comment on lines +1880 to +1881

		check(_ast.AST(), size('P'))
		with self.assertWarns(DeprecationWarning):
		check(_ast.AST(), size('P'))

JelleZijlstra Oct 20, 2025

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I think it's here because it's arguably testing sys.getsizeof. Maybe it could be changed to test a concrete AST class instead?

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bedevere-app Bot added awaiting merge and removed awaiting review labels

Oct 20, 2025

brianschubert added 4 commits

October 26, 2025 21:10


          Merge remote-tracking branch 'upstream/main'

250c33c


          Merge branch 'main' into pythongh-116021-ast-depr-abstract

f8c0aef


          Merge branch 'main'

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          Update test_sys per review

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brianschubert requested review from JelleZijlstra and picnixz

February 22, 2026 21:15

JelleZijlstra reviewed

Feb 22, 2026

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Parser/asdl_c.py Resolved

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brianschubert and others added 2 commits

February 22, 2026 17:20


          Update Parser/asdl_c.py

b7100a4

Co-authored-by: Jelle Zijlstra <[email protected]>


          Regen Python-ast.c

202a372

Eclips4 approved these changes

Mar 1, 2026

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This PR is stale because it has been open for 30 days with no activity.

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github-actions Bot added the stale Stale PR or inactive for long period of time. label

Apr 28, 2026


          Merge branch 'main' into pythongh-116021-ast-depr-abstract

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JelleZijlstra merged commit bdedc4a into python:main

May 2, 2026

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newville mentioned this pull request

Oct 2, 2026

Python 3.15 checks and updates lmfit/asteval#159

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brianschubert commented Aug 16, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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brianschubert commented Aug 16, 2025 •

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brianschubert Aug 16, 2025 •

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