René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"annotationlib: `ref.evaluate(format=Format.FORWARDREF)` returns a ForwardRef with a copied `__globals__` that no longer updates","articleBody":"# Bug report\n\n### Bug description:\n\nThis can happen internally in `get_annotations` and means subsequent attempts to evaluate it will fail even if the names have since been defined.\n\nUnderlying logic:\n```python\nfrom annotationlib import get_annotations, Format\n\nclass Demo:\n    x: Sequence[undefined]\n\nannos = get_annotations(Demo, format=Format.FORWARDREF)\n\nx_anno = annos['x']\n\n# Try to evaluate the reference, but just give a forwardref if it fails\nx_repeat_anno = x_anno.evaluate(format=Format.FORWARDREF)\n\n# The resulting reference no longer shares the globals namespace with the annotate function\nprint(f\"{x_anno.__globals__ is Demo.__annotate__.__globals__ = }\")  # True\nprint(f\"{x_repeat_anno.__globals__ is Demo.__annotate__.__globals__ = }\")  # False\n\n# Define the previously undefined attributes\nfrom collections.abc import Sequence\nundefined = str\n\n# This means evaluation fails in the second case\nprint(f\"{x_anno.evaluate() = }\")  # collections.abc.Sequence[str]\nprint(f\"{x_repeat_anno.evaluate() = }\")  # NameError\n```\n\nThis `evaluate` call happens internally if `get_annotations` has to rely on the fallback behaviour for an unexpected exception, such as an `AttributeError`:\n\n```python\nfrom annotationlib import get_annotations, Format\nimport typing\n\nclass Works:\n    a: Sequence[undefined]\n    b: unknowable\n\n# Intentionally set up an annotation that will raise AttributeError on evaluation\nclass Fails:\n    a: Sequence[undefined]\n    b: typing.doesnotexist\n\na_works = get_annotations(Works, format=Format.FORWARDREF)['a']\na_fails = get_annotations(Fails, format=Format.FORWARDREF)['a']\n\n# Realise the references\nfrom collections.abc import Sequence\nundefined = str\n\nprint(f\"{a_works.evaluate() = }\")  # collections.abc.Sequence[str]\nprint(f\"{a_fails.evaluate() = }\")  # NameError\n```\n\nThis appears to be caused by the creation of a new globals dict here:\nhttps://github.com/python/cpython/blob/e39255e76d4b6755a44f6d4e63180136c778d2a5/Lib/annotationlib.py#L164-L167\n\nCommenting this out makes these examples succeed, but obviously breaks type parameters.\n\n### CPython versions tested on:\n\nCPython main branch, 3.14\n\n### Operating systems tested on:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-138075\n* gh-140929\n* gh-140930\n* gh-140931\n* gh-140974\n* gh-141527\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/DavidCEllis","@type":"Person","name":"DavidCEllis"},"datePublished":"2025-08-19T19:45:53.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/137969/cpython/issues/137969"}