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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Raise consistent `NameError` in `ForwardRef.evaluate()`","articleBody":"# Feature or enhancement\n\n### Proposal:\n\nThe new `ForwardRef.evaluate()` implementation had a fast path introduced in https://github.com/python/cpython/pull/124337 to _not_ call `eval()`:\n\nhttps://github.com/python/cpython/blob/cb394101110e13a27e08bbf2fe9f38d847db004c/Lib/annotationlib.py#L177-L187\n\nHowever, when the `NameError` is raised, the format is different from the one raised by `eval()`:\n\nThe exception message is defined as:\n\nhttps://github.com/python/cpython/blob/cb394101110e13a27e08bbf2fe9f38d847db004c/Python/ceval_macros.h#L308\n\nand raised this way:\n\nhttps://github.com/python/cpython/blob/cb394101110e13a27e08bbf2fe9f38d847db004c/Python/ceval.c#L3339-L3351\n\nTo have consistent exceptions raised, would it be possible to change the Python fast path implementation to match the C eval code?\n\n```diff\ndiff --git a/Lib/annotationlib.py b/Lib/annotationlib.py\nindex 731817a9973..c83a1573ccd 100644\n--- a/Lib/annotationlib.py\n+++ b/Lib/annotationlib.py\n@@ -27,6 +27,9 @@ class Format(enum.IntEnum):\n \n \n _sentinel = object()\n+# Following `NAME_ERROR_MSG` in `ceval_macros.h`:\n+_NAME_ERROR_MSG = \"name '{name:.200}' is not defined\"\n+\n \n # Slots shared by ForwardRef and _Stringifier. The __forward__ names must be\n # preserved for compatibility with the old typing.ForwardRef class. The remaining\n@@ -184,7 +187,7 @@ def evaluate(\n             elif is_forwardref_format:\n                 return self\n             else:\n-                raise NameError(arg)\n+                raise NameError(_NAME_ERROR_MSG.format(name=arg), name=arg)\n         else:\n             code = self.__forward_code__\n             try:\n```\n\nThis requires `_NAME_ERROR_MSG` to be in sync with the one from `ceval_macros.h`.\n\nOr at least, the `NameError` should have its `name` property set (especially as type stubs shows `NameError.name` as `str` currently).\n\ncc @JelleZijlstra.\n\n### Has this already been discussed elsewhere?\n\nThis is a minor feature, which does not need previous discussion elsewhere\n\n### Links to previous discussion of this feature:\n\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-135663\n* gh-135673\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/Viicos","@type":"Person","name":"Viicos"},"datePublished":"2025-06-17T22:49:54.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/135646/cpython/issues/135646"}