(🎁) `isinstance`/`issubclass` only accept `typing.Union`s of `type`s, not other type forms
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Description
Until type forms are properly supported by the type system, I wonder if this could be special cased?
from typing import Any
isinstance(1, str | Any) # no error, fails at runtime with TypeError: typing.Any cannot be used with issubclass()
FYI mypy is incorrectly inferring this as a types.UnionType but it is actually a typing.Union(#12369), I don't think you can have a UnionType with type forms in it.
PyCharm correctly warns here:
related: python/typeshed/issues/7505
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Research direction
Reproduce the isinstance(1, str | Any) example and compare mypy's inferred types.UnionType with the runtime behavior described in the issue. Read the related typeshed issue #7505 and trace the type-checking path for isinstance and issubclass; done means the supported type forms are handled consistently without permitting the reported invalid case.
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Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100