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match: Incorrect "Incompatible types in capture pattern" when type has already been narrowed #16736

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JelleZijlstra opened this issue Jan 2, 2024 · 0 comments · May be fixed by #18155
Open

match: Incorrect "Incompatible types in capture pattern" when type has already been narrowed #16736

JelleZijlstra opened this issue Jan 2, 2024 · 0 comments · May be fixed by #18155
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bug mypy got something wrong topic-match-statement Python 3.10's match statement

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@JelleZijlstra
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x: int | None
y: int
match x:
    case None:
        pass
    case y:
        pass
main.py:6: error: Incompatible types in capture pattern (pattern captures type "int | None", variable has type "int")  [misc]

https://mypy-play.net/?mypy=latest&python=3.10&gist=b3423e1eab3afadc8e4d172761d256a2

This should be fine, because the previous case ensured that y is not None.

I ran into this in a real use case.
@JelleZijlstra JelleZijlstra added bug mypy got something wrong topic-match-statement Python 3.10's match statement labels Jan 2, 2024
@shenyih0ng shenyih0ng linked a pull request Nov 14, 2024 that will close this issue
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bug mypy got something wrong topic-match-statement Python 3.10's match statement
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Fix incorrect "Incompatible types in capture pattern" error for narrowed types shenyih0ng/mypy
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@JelleZijlstra