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typing: forward references don't understand special type forms #90697
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Consider the following code on 3.11 main:
Currently, the My understanding is this is because when typing._type_check runs on a type where special forms are allowed it's possible for the typing._type_convert it calls it itself run a typing._type_check on contained forward references. However, if that forward reference was itself a special form then it's possible to get an error because typing._type_check doesn't pass on that special forms are allowed. I have drafted a patch to pass on this information. This will become important in the future as more special forms are allowed to wrap each other, such as allowing Final and ClassVar to nest each other in dataclasses, or when Required and NotRequired land. In the future we may also want to reconsider runtime restrictions on special forms in Is my analysis/patch approach okay? Forward references can be tricky. Should we be discussing runtime restrictions in typing.py more generally in the future? |
typo: the line is |
I wonder if this is at all similar to bpo-41370. |
I did try the proposed patch in bpo-41370 and verified it didn't resolve the issue so I'm not certain they strictly overlap, but I also haven't had time to fully digest the underlying issues in bpo-41370 yet. I think it does have relevance for changes we want to make for dataclasses re: Annotated, though: https://bugs.python.org/issue46511 |
Agree it's not the same issue, but there's similarity -- both are due to putting a stringized annotation (presumably a forward ref) somewhere inside another construct. whether it's list["N"] or Annotated["ClassVar[int]"]. |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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