gh-133960: Improve typing.evaluate_forward_ref #133961
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As explained in python#133960, this removes most of the behavior differences with ForwardRef.evaluate. The remaining difference is about recursive evaluation of forwardrefs; this is practically useful in cases where an annotation refers to a type alias that itself is string-valued. This also improves several edge cases that were previously not handled optimally. For example, the function now takes advantage of the partial evaluation behavior of ForwardRef.evaluate() to evaluate more ForwardRefs in the FORWARDREF format. This also fixes python#133959 as a side effect, because the buggy behavior in python#133959 derives from evaluate_forward_ref().
AlexWaygood
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May 25, 2025
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| A = "str" | ||
| ref = ForwardRef('list[A]') | ||
| with self.assertRaises(NameError): | ||
| typing.evaluate_forward_ref(ref) |
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remind me why this needs to raise NameError? Does the globals argument not default to the globals of the module calling evaluate_forward_ref? I think that's what I'd naively expect.
The docs for typing.evaluate_forward_ref point me towards https://docs.python.org/3.14/library/annotationlib.html#annotationlib.ForwardRef.evaluate for information on these parameters, but the docs there are silent on what happens if globals is None and owner is None
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It eventually defaults to empty globals. I think that's right for most use cases; usually you'll be evaluating a ForwardRef in a library that came from some user code, and the globals of the module where you're doing the evaluating aren't a particularly good place to look for data.
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I'll make a separate PR adding this to the annotationlib docs
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
AlexWaygood
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Thanks @JelleZijlstra for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14. |
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As explained in pythonGH-133960, this removes most of the behavior differences with ForwardRef.evaluate. The remaining difference is about recursive evaluation of forwardrefs; this is practically useful in cases where an annotation refers to a type alias that itself is string-valued. This also improves several edge cases that were previously not handled optimally. For example, the function now takes advantage of the partial evaluation behavior of ForwardRef.evaluate() to evaluate more ForwardRefs in the FORWARDREF format. This also fixes pythonGH-133959 as a side effect, because the buggy behavior in pythonGH-133959 derives from evaluate_forward_ref(). (cherry picked from commit 57fef27) Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
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GH-134663 is a backport of this pull request to the 3.14 branch. |
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…34663) gh-133960: Improve typing.evaluate_forward_ref (GH-133961) As explained in GH-133960, this removes most of the behavior differences with ForwardRef.evaluate. The remaining difference is about recursive evaluation of forwardrefs; this is practically useful in cases where an annotation refers to a type alias that itself is string-valued. This also improves several edge cases that were previously not handled optimally. For example, the function now takes advantage of the partial evaluation behavior of ForwardRef.evaluate() to evaluate more ForwardRefs in the FORWARDREF format. This also fixes GH-133959 as a side effect, because the buggy behavior in GH-133959 derives from evaluate_forward_ref(). (cherry picked from commit 57fef27) Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
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Refer to python/cpython#133961 I copied the tests from Python 3.14. Two don't pass but could probably be made to pass by backporting more of annotationlib, but that's more than I think we should do now. Fixes python#608
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Refer to python/cpython#133961 I copied the tests from Python 3.14. Two don't pass but could probably be made to pass by backporting more of annotationlib, but that's more than I think we should do now. Fixes #608
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As explained in #133960, this removes most of the behavior differences with ForwardRef.evaluate.
The remaining difference is about recursive evaluation of forwardrefs; this is practically useful
in cases where an annotation refers to a type alias that itself is string-valued.
This also improves several edge cases that were previously not handled optimally. For example,
the function now takes advantage of the partial evaluation behavior of ForwardRef.evaluate() to
evaluate more ForwardRefs in the FORWARDREF format.
This also fixes #133959 as a side effect, because the buggy behavior in #133959 derives from
evaluate_forward_ref().
typing.evaluate_forward_ref#133960📚 Documentation preview 📚: https://cpython-previews--133961.org.readthedocs.build/