mypy infers the wrong type for classmethods

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Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
停滞
技术栈
python
领域
devtools

调研方向

Start with the simplified classmethod example and compare mypy's inferred type for hi with the classmethod annotation in typeshed's stdlib/3/builtins.pyi. Trace the callable inference path to determine whether the real classmethod type can be preserved, and use a focused regression test for the __func__ access as the completion check.

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描述

bug topic-descriptors topic-runtime-semantics

We have some code that simplifies to this:

class A:
    @classmethod
    def hi(cls):
        pass

    bye = classmethod(hi.__func__)

(The real code is wrapping an async classmethod with a sync version; there's another async-to-sync wrapper in there.)

Mypy doesn't like this code because it doesn't know that classmethods have a __func__ attribute. The typeshed annotation for classmethod includes __func__, but mypy doesn't infer the real classmethod type for hi (which is the actual type at runtime), it just infers a general callable type.

This may not be easily fixed until we have protocol support and can more easily have various callable subtypes?

I'm also OK if this is closed as "just use cast() if you're accessing private attributes of a classmethod"; it's certainly not high priority.

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