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Incompatible signature in method with restricted overload for a generic class #12151
Description
Bug Report
When a method of a generic class has an overload for a particular type of the generic parameter, subclasses that don't have that particular value should be able to override the method without that overload, but currently aren't.
To Reproduce
Consider the following code:
T = TypeVar("T")
A_no_T = TypeVar(
"A_no_T",
bound="A[None]",
)
class A(
Generic[T],
):
@overload
def method(
self: A_no_T,
) -> None:
pass
@overload
def method(
self,
t: T,
) -> None:
pass
def method(
self,
t: Optional[T] = None,
) -> None:
return
class B(A[int]):
def method(
self,
t: int,
) -> None:
passExpected Behavior
The code should typecheck without errors.
Actual Behavior
The following error is raised
Mypy: Signature of "method" incompatible with supertype "A" [override]
Superclass:
@overload
def method(self) -> None
@overload
def method(self, t: int) -> None
Subclass:
def method(self, t: int) -> None
Your Environment
- Mypy version used: 0.931
- Mypy command-line flags: --follow-imports=silent --show-column-numbers --show-error-codes
- Mypy configuration options from
mypy.ini(and other config files):
strict = True
strict_equality = True
implicit_reexport = True - Python version used: 3.8.0
- Operating system and version: Linux Ubuntu 18.04.6 LTS
Activity
erictraut commentedon Feb 8, 2022
I don't think that's generally safe. What if the base class
Acontains the following?Now if you call
B().other_method(), the functionB.methodwill get called with aNoneargument.The problem is that when analyzing
A, we don't know whetherThas been bound toNone, so the trick you're using to detectA[None]doesn't work in this case.vnmabus commentedon Feb 8, 2022
Sorry, but I don't get it. Surely
xshould have anintvalue inB, no?erictraut commentedon Feb 8, 2022
Sorry, forget what I said. My analysis was incorrect.
I think the issue is that mypy is validating the method implementation signature in the child class against the implementation signature in the parent class, but you want it to take into account the overload signatures in the child class as well.
vnmabus commentedon Feb 8, 2022
Yeah, I think that is something sensible to do. In fact, requiring me to provide the first overload is wrong.
erictraut commentedon Aug 13, 2023
I think this bug has been fixed. The latest version of mypy (1.5) no longer generates an error.
hauntsaninja commentedon Aug 13, 2023
I fixed this in #14882