isinstance(x, Type) not accepted

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#3,060 6 comments 6 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
compilers

Research direction

No file, test, or entry point is named. Start by reproducing the shown isinstance(x, Type) example in mypy, then trace how the second argument to isinstance is validated. Done means the example no longer produces the incompatible-type error while existing isinstance checks remain correctly validated.

Written by the indexing model from the issue text.

Description

bug false-positive priority-1-normal topic-runtime-semantics topic-type-narrowing topic-usability

isinstance(x, Type) generates in an error, even though it should probably be considered equivalent to isinstance(x, type). Example:

from typing import Type

def f(x: Type[int]) -> None:
    if isinstance(x, Type):  # Argument 2 to "isinstance" has incompatible type "object"; 
                             # expected "Union[type, Tuple[Union[type, Tuple[Any, ...]], ...]]"
        pass
Dominant language
Python
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Avg merge
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Merged PRs (30d)
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