Errors on @overload in supertype signatures
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Description
Bug Report
Given ABC A which have two implementations B and C. Method C.view() may return either B or C, depending on argument type. When using @overload to describe this, mypy complains with "Signature of "view" incompatible with supertype "A"". However, the type annotations provided by the overload works as expected.
To Reproduce
from __future__ import annotations
from abc import ABC, abstractmethod
from typing import overload, reveal_type
class A(ABC):
@abstractmethod
def view(self, x: int | None = None) -> A: ...
class B(A):
def view(self, x: int | None = None) -> B:
return B()
class C(A):
@overload # mypy complains: "Signature of "view" incompatible with supertype "A""
def view(self, x: int) -> B: ...
@overload
def view(self, x: None = None) -> C: ...
def view(self, x: int | None = None) -> B | C:
if x is None:
return C()
else:
return B()
# This works as expected when @overload is used
reveal_type(C().view(None)) # Revealed type is C
reveal_type(C().view(5)) # Revealed type is B
https://gist.github.com/mypy-play/00b068b5b6eeebbea6f9486dba468708
Actual Behavior
main.py:14: error: Signature of "view" incompatible with supertype "A" [override]
main.py:14: note: Superclass:
main.py:14: note: def view(self, x: int | None = ...) -> A
main.py:14: note: Subclass:
main.py:14: note: @overload
main.py:14: note: def view(self, x: int) -> B
main.py:14: note: @overload
main.py:14: note: def view(self, x: None = ...) -> C
Your Environment
- Mypy version used: 1.19.0
- Mypy command-line flags: Default args in gist
- Mypy configuration options from
mypy.ini(and other config files): - Python version used: Python 3.12
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the provided Python reproducer with mypy 1.19.0 and inspect the overload and supertype-signature compatibility check. Done means the example no longer reports an incompatible override while reveal_type still reports C for None and B for 5.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100