attrs: Inheritance breaks mypy type checking with optional attributes if Generics are involved #13794
Description
Inheritance breaks mypy type checking with optional attributes if Generics are involved:
from typing import Generic, Optional, TypeVar
import attr
T = TypeVar("T")
@attr.mutable()
class Parent(Generic[T]): # Removing `Generic` here and `[float]` below doesn't show `mypy` issues anymore
run_type: Optional[int] = None
@attr.mutable()
class Child(Parent[float]):
pass
Parent(
run_type =None,
)
Child(
run_type =None, # error: Argument "run_type" to "Child" has incompatible type "None"; expected "int" [arg-type]
)
There is an error displayed which is wrong. Doing the same without any Generic involved works as expected.
Not quite sure if this is a mypy issue or an attrs typing issue.
It seems to check fine in older mypy versions (eg 0.950), but breaks in the newest (0.981).
See also: python-attrs/attrs#1028