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GeezerVison is showing github.com — gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef by DavidCEllis · Pull Request #148682 · python/cpython

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DavidCEllis commented Apr 17, 2026 •

edited by bedevere-app Bot

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This adds a new ForwardRef.__resolved_forward_str__ attribute which takes the __forward_arg__ and replaces any internal __annotationlib_name_x__ names with the type_repr of the object they represent.

Before:

ForwardRef('ref | __annotationlib_name_1__', is_class=True, owner=<class '__main__.Example'>)
ref | __annotationlib_name_1__

After:

ForwardRef('ref | str', is_class=True, owner=<class '__main__.Example'>)
ref | str

This approach replaces the extra_names with their type_repr when the forwardref is evaluated to a string. I'm fairly sure that trying to get the original names as they are in the source would be both slower and significantly more complicated.

This logic is largely based on something I already have for my reannotate library.

Issue: annotationlib - evaluating forward references in STRING format can 'leak' internal names #148680

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DavidCEllis added 3 commits

April 17, 2026 12:52


          Add tests for replacement of extra names in repr and string evaluation

12d7a45


          Replace names from __extra_names__ when evaluating forward references…

e1e258e

… as strings


          Try to write a clearer comment

ade5f8e

DavidCEllis requested a review from JelleZijlstra as a code owner

April 17, 2026 12:37

bedevere-app Bot added the awaiting review label

Apr 17, 2026

bedevere-app Bot mentioned this pull request

Apr 17, 2026

annotationlib - evaluating forward references in STRING format can 'leak' internal names #148680

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JelleZijlstra reviewed

Apr 17, 2026

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Lib/test/test_annotationlib.py Resolved

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JelleZijlstra reviewed

Apr 17, 2026

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Lib/annotationlib.py

		resolved_str = type_repr(name_obj)
		else:
		visitor = _ExtraNameFixer(names)
		ast_expr = ast.parse(resolved_str, mode="eval").body

JelleZijlstra Apr 17, 2026

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We might need to cache this, it's probably pretty slow. What do you think?

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DavidCEllis Apr 17, 2026

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This is in fact, not very fast. Definitely worth caching if it's going to be accessed frequently.

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DavidCEllis Apr 17, 2026

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>>> a_anno
ForwardRef('unknown | str | int | list[str] | tuple[int, ...]', is_class=True, owner=<class '__main__.Example'>)
>>> b_anno
ForwardRef('unknown', is_class=True, owner=<class '__main__.Example'>)

>>> a = timeit(lambda: a_anno.__resolved_forward_str__, number=10_000)
>>> b = timeit(lambda: b_anno.__resolved_forward_str__, number=10_000)
>>> a
0.18359258100008446
>>> b
0.0018204959997092374
>>> a / b
100.8475607907994

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DavidCEllis Apr 20, 2026

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I've added a cache and ended up shortening the name of the property and the cache. Adding the cache did mean adding an extra slot to both classes.

Not completely sold on the names I have if you have something better.

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DavidCEllis added 2 commits

April 17, 2026 16:15


          Make the repr test use retrieved rather than 'artificial' forward ref…

f3b6293

…erences


          Add a cache for resolved str, test the cache is used, shorten names

675738a

ashm-dev reviewed

Apr 20, 2026

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Lib/annotationlib.py Resolved

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Lib/annotationlib.py Resolved

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DavidCEllis and others added 4 commits

April 20, 2026 22:48


          Update Lib/annotationlib.py

5a36751

Fix a misplaced parenthesis that incorrectly caused a statement to evaluate as truthy

Co-authored-by: Shamil <[email protected]>


          remove unnecessary and incorrect node 'fixup'.

3d9b64a


          Remove optimization for a condition that should never be hit normally

57bfa41


          Remove 'synthetic' test, make the regular test replace additional values

3d08f8f

JelleZijlstra approved these changes

Apr 23, 2026

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Looks good, but could you add a NEWS entry?

We'll also have to decide whether to backport to 3.14. I'm leaning towards yes, because the old behavior seems genuinely buggy.

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

Apr 23, 2026

blurb-it Bot and others added 2 commits

April 23, 2026 07:38


          📜🤖 Added by blurb_it.

5de5e01


          Fix linting issue (maybe)

4ff6eeb

JelleZijlstra added the needs backport to 3.14 bugs and security fixes label

Apr 23, 2026

JelleZijlstra merged commit 158dbbb into python:main

Apr 23, 2026

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miss-islington-app Bot commented Apr 23, 2026

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Thanks @DavidCEllis for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

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bedevere-app Bot removed the awaiting merge label

Apr 23, 2026

bedevere-app Bot commented Apr 23, 2026

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GH-148913 is a backport of this pull request to the 3.14 branch.

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bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label

Apr 23, 2026

JelleZijlstra pushed a commit that referenced this pull request

Apr 23, 2026


          [3.14] gh-148680: Replace internal names with type_reprs of objects i…

b6a7212

…n string representations of ForwardRef (GH-148682) (#148913)

(cherry picked from commit 158dbbb)

Co-authored-by: David Ellis <[email protected]>
Co-authored-by: Shamil <[email protected]>

ljfp pushed a commit to ljfp/cpython that referenced this pull request

Apr 25, 2026


          pythongh-148680: Replace internal names with type_reprs of objects in…

… string representations of ForwardRef (python#148682)

Co-authored-by: Shamil <[email protected]>

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DavidCEllis commented Apr 17, 2026 • edited by bedevere-app Bot Loading Uh oh! There was an error while loading. Please reload this page.

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DavidCEllis commented Apr 17, 2026 •

edited by bedevere-app Bot

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