lambda input type is Any when function type is a union, and no error when lambda does not satisfy any of the types in the union #13036

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1. DetachHead

   added

   bugmypy got something wrongmypy got something wrong

   on Jun 28, 2022
2. AlexWaygood

   added

   topic-inferenceWhen to infer types or require explicit annotationsWhen to infer types or require explicit annotations

   on Jun 28, 2022
3. erictraut commented on Aug 13, 2023

   

   erictraut

   on Aug 13, 2023

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   The title of this bug is misleading. The real bug here is that mypy doesn't report a type violation for f(lambda x: x). This lambda doesn't satisfy either Callable[[int], None] or Callable[[int, str], None], so it should be flagged as a type violation.
4. DetachHead commented on Aug 13, 2023

   

   DetachHead

   on Aug 13, 2023

   Last edited by DetachHead

   ContributorAuthor

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   it still happens when the lambda does satisfy one of the types in the union:

   from typing import Callable
   def f(a: Callable[[int], int] | Callable[[int, str], None]) -> None: ...
   
   f(lambda x: reveal_type(x))  # Any

   i guess that was a mistake in my original post but that means there are two different issues here
5. DetachHead

   changed the title [-]lambda input type is `Any` when function type is a union[/-] [+]lambda input type is `Any` when function type is a union, and no error when lambda does not satisfy any of the types in the union[/+] on Aug 13, 2023