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Decorated method type-incompatibility with superclass #5836
Description
I'm raising a bug.
It's also posted on SO at https://stackoverflow.com/q/52744713/5986907
I get
$ mypy file.py python.py:34: error: Signature of "fn" incompatible with supertype "B"
for file.py
from typing import Callable, TypeVar, cast
T = TypeVar('T')
def dec(f: Callable[..., T]) -> T:
def p(self):
return getattr(self, '_' + f.__name__)
return cast(T, property(p))
class X:
pass
class Y(X):
pass
class A:
_fn = Y()
class B(A):
@dec
def fn(self) -> X:
return X()
class C(B):
@dec
def fn(self) -> Y:
return Y()
I'd expect there to be no error as Y is a subclass of X.
I've tried this with mypy 0.630 and Python 3.5.2, 3.6.6 and 3.7.0. Also with mypy git master for python 3.5.2 and 3.7.0
It's possible these are related but I couldn't quite connect them
#220
#4430
Activity
ilevkivskyi commented on Oct 25, 2018
Hm, it still fails on master, this is because of this code:
I think this is easy to fix by replacing is_equivalent with is_subtype at least for effectively read-only attributes. Anyway mypy currently allows covariant overriding for mutable attributes although this is technically unsafe, see #3208
Fix covariant overriding of decorated methods (#8350)