I have this code: class A: def f(self, a: int) -> int: raise NotImplementedError class B(A): def f(self, a): return a However mypy --strict tells me that B.f "is missing a type annotation". It seems obvious to me that B.f has the same types as A.f, especially given that mypy shows me an error if I try to put different ones: class B(A): def f(self, a: bool) -> str: return str(a) error: Return type "str" of "f" incompatible with return type "int" in supertype "A" [override] error: Argument 1 of "f" is incompatible with supertype "A"; supertype defines the argument type as "int" [override] note: This violates the Liskov substitution principle note: See https://mypy.readthedocs.io/en/stable/common_issues.html#incompatible-overrides Since mypy already knows the expected types of B.f, why does it force me to re-declare them? Is there some way to avoid it? Continue reading...
