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Presence of property in Protocol causes false positive in multiple inheritance scenario #16873

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slanzmich opened this issue Feb 5, 2024 · 3 comments
Closed

Presence of property in Protocol causes false positive in multiple inheritance scenario #16873

slanzmich opened this issue Feb 5, 2024 · 3 comments
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bug mypy got something wrong topic-protocols

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@slanzmich
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Bug Report

I'm getting a false positive from the following example

from typing import Protocol
from typing_extensions import Self

class P(Protocol):
    # Removing the property makes the problem disappear
    @property
    def x(self) -> int: ...

    def clone(self) -> Self: ...

class A:
    def clone(self) -> Self:
        return self

class B(A, P):
    @property
    def x(self) -> int:
        return 100
main.py:18: error: Definition of "clone" in base class "A" is incompatible with definition in base class "P"  [misc]

Obviously, A.clone does not actually clone the instance, but that is left out for clarity.

The false positive is not reported when I remove the property x from the protocol P.

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.12&gist=fe15d8bc18aa7b61feb3e56fce615f47
@slanzmich slanzmich added the bug mypy got something wrong label Feb 5, 2024
@hauntsaninja
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Thanks, looks like it's not just property, basically anything else in the Protocol seems to trigger the error:

from typing import Protocol, Self

class P(Protocol):
    def foo(self) -> None: ...
    def clone(self) -> Self: ...

class A:
    def clone(self) -> Self: ...

class B(A, P):
    pass

(As a workaround you can consider not explicitly inheriting from the protocol)

@sterliakov
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This passes on current master and was fixed by #18465 - sorry, I missed more than one related issue...

@hauntsaninja
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Great!

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@hauntsaninja @slanzmich @sterliakov @AlexWaygood