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gh-138764: annotationlib - Make call_annotate_function fallback to using VALUE annotations if both the requested format and VALUE_WITH_FAKE_GLOBALS are not implemented#138803

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DavidCEllis:fix-fake-globals-calls-fallback-value
Oct 21, 2025
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@DavidCEllis DavidCEllis commented Sep 11, 2025 •
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Alternative to #138788 - instead of raising the NotImplementedError this falls back to calling an annotate function with Format.VALUE if both the specified format and Format.VALUE_WITH_FAKE_GLOBALS are both not implemented.

I think this may be more useful behaviour than #138788 ?

If VALUE also fails, then the only option was failure from the start. I think it's more consistent to raise the error from VALUE annotations in that case.

Using the examples from the other PR:

from annotationlib import Format, call_annotate_function

def annotate(format, /):
    if format == Format.VALUE:
        return {'x': str}
    else:
        raise NotImplementedError(format)

print(call_annotate_function(annotate, Format.STRING))

On main, and with this patch:

{'x': 'str'}
from annotationlib import Format, call_annotate_function

def annotate(format, /):
    if format in {Format.VALUE}:
        return {'x': str}
    else:
        raise NotImplementedError(format)

print(call_annotate_function(annotate, Format.STRING))

Main:

TypeError: exceptions must derive from BaseException

Patch:

{'x': 'str'}

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DavidCEllis commented Sep 11, 2025

I also prefer this over #138788 because I think FORWARDREF and STRING annotations should always work if VALUE annotations work.

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JelleZijlstra commented Sep 11, 2025

I like this too. We might need to extend the listing under https://docs.python.org/3.14/library/annotationlib.html#annotationlib.get_annotations explaining how the different formats work (and in any case, this needs a NEWS entry).

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DavidCEllis commented Sep 12, 2025

I had a go at extending the descriptions of the formats. This made me realise I was describing behaviour that there wasn't a test for as a fall back so added some extra tests.

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JelleZijlstra approved these changes Oct 20, 2025
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Looks good, left some small tweaks.

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Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
@JelleZijlstra JelleZijlstra added the needs backport to 3.14 bugs and security fixes label Oct 21, 2025
@JelleZijlstra JelleZijlstra enabled auto-merge (squash) October 21, 2025 15:31
@JelleZijlstra JelleZijlstra merged commit 95c257e into python:main Oct 21, 2025
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miss-islington-app bot commented Oct 21, 2025

Thanks @DavidCEllis for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Oct 21, 2025
@DavidCEllis @miss-islington
pythongh-138764: annotationlib: Make call_annotate_function fallbac…
fe9be14 
…k to using `VALUE` annotations if both the requested format and `VALUE_WITH_FAKE_GLOBALS` are not implemented (pythonGH-138803)

(cherry picked from commit 95c257e)

Co-authored-by: David Ellis <ducksual@gmail.com>
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bedevere-app bot commented Oct 21, 2025

GH-140426 is a backport of this pull request to the 3.14 branch.

@bedevere-app bedevere-app bot removed the needs backport to 3.14 bugs and security fixes label Oct 21, 2025
JelleZijlstra pushed a commit that referenced this pull request Oct 21, 2025
@miss-islington @DavidCEllis
[3.14] gh-138764: annotationlib: Make call_annotate_function fallba…
c7fda9b 
…ck to using `VALUE` annotations if both the requested format and `VALUE_WITH_FAKE_GLOBALS` are not implemented (GH-138803) (#140426)

gh-138764: annotationlib: Make `call_annotate_function` fallback to using `VALUE` annotations if both the requested format and `VALUE_WITH_FAKE_GLOBALS` are not implemented (GH-138803)
(cherry picked from commit 95c257e)

Co-authored-by: David Ellis <ducksual@gmail.com>
StanFromIreland pushed a commit to StanFromIreland/cpython that referenced this pull request Dec 6, 2025
@DavidCEllis @StanFromIreland
pythongh-138764: annotationlib: Make call_annotate_function fallbac…
6e7d77c 
…k to using `VALUE` annotations if both the requested format and `VALUE_WITH_FAKE_GLOBALS` are not implemented (python#138803)
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