gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef by DavidCEllis · Pull Request #148682 · python/cpython · GitHub

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

… as strings

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

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

>>> 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

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.

…erences

Fix a misplaced parenthesis that incorrectly caused a statement to evaluate as truthy Co-authored-by: Shamil <ashm.tech@proton.me>

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.

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

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

…n string representations of ForwardRef (GH-148682) (#148913) (cherry picked from commit 158dbbb) Co-authored-by: David Ellis <ducksual@gmail.com> Co-authored-by: Shamil <ashm.tech@proton.me>

… string representations of ForwardRef (python#148682) Co-authored-by: Shamil <ashm.tech@proton.me>

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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Comment thread Lib/test/test_annotationlib.py

JelleZijlstra reviewed Apr 17, 2026

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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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Comment thread Lib/annotationlib.py Outdated

Comment thread Lib/annotationlib.py Outdated

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 <ashm.tech@proton.me>

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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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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bedevere-app Bot removed the awaiting merge label Apr 23, 2026

bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Apr 23, 2026

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…

2848310

… string representations of ForwardRef (python#148682) Co-authored-by: Shamil <ashm.tech@proton.me>

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

gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef by DavidCEllis · Pull Request #148682 · python/cpython · GitHub

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gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef#148682
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DavidCEllis:fix-forwardref-string-names

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gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef by DavidCEllis · Pull Request #148682 · python/cpython · GitHub

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gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef - #148682

gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef#148682JelleZijlstra merged 11 commits intopython:mainpython/cpython:mainfrom DavidCEllis:fix-forwardref-string-namesDavidCEllis/cpython:fix-forwardref-string-namesCopy head branch name to clipboard

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gh-148680: Replace internal names with type_reprs of objects in string representations of ForwardRef#148682
JelleZijlstra merged 11 commits into
python:mainfrom
DavidCEllis:fix-forwardref-string-names

DavidCEllis commented Apr 17, 2026 •
edited by bedevere-app Bot
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