False positive when calling a method from a subclass #15097
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bug
mypy got something wrong
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cdce8p
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May 31, 2025
Fixes python#18024 Fixes python#18706 Fixes python#17734 Fixes python#15097 Fixes python#14814 Fixes python#14806 Fixes python#14259 Fixes python#13041 Fixes python#11993 Fixes python#9585 Fixes python#9266 Fixes python#9202 Fixes python#5481 This is a fourth "major" PR toward python#7724. This is one is watershed/crux of the whole series (but to set correct expectations, there are almost a dozen smaller follow-up/clean-up PRs in the pipeline). The core of the idea is to set current type-checker as part of the global state. There are however some details: * There are cases where we call `is_subtype()` before type-checking. For now, I fall back to old logic in this cases. In follow up PRs we may switch to using type-checker instances before type checking phase (this requires some care). * This increases typeops import cycle by a few modules, but unfortunately this is inevitable. * This PR increases potential for infinite recursion in protocols. To mitigate I add: one legitimate fix for `__call__`, and one temporary hack for `freshen_all_functions_type_vars` (to reduce performance impact). * Finally I change semantics for method access on class objects to match the one in old `find_member()`. Now we will expand type by instance, so we have something like this: ```python class B(Generic[T]): def foo(self, x: T) -> T: ... class C(B[str]): ... reveal_type(C.foo) # def (self: B[str], x: str) -> str ``` FWIW, I am not even 100% sure this is correct, it seems to me we _may_ keep the method generic. But in any case what we do currently is definitely wrong (we infer a _non-generic_ `def (x: T) -> T`). --------- Co-authored-by: hauntsaninja <hauntsaninja@gmail.com> Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
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Bug Report
I encounter a false positive using mypy when a Generic class indirectly calls a method defined in its GrandParent.
To Reproduce
Expected Behavior
No error when running mypy.
Actual Behavior
I get this error:
error: Argument 1 to "say_hello" of "Grandparent" has incompatible type "Child[T]"; expected "Grandparent[T]" [arg-type]Removing the Generic types, calling
Grandparent.say_hello(self)from the child, redefining the method in the Parent fixes the error.Your Environment
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