False positive: subclass method of overloaded function

[SubaruArai]

Bug Report

Mypy reports error when a subclass overwrites a overloaded method.

To Reproduce

Gist URL
Playground URL

Expected Behavior

This should be fine

Actual Behavior

dum.py:18: error: Signature of "method" incompatible with supertype "SuperClass"  [override]
dum.py:18: note:      Superclass:
dum.py:18: note:          @overload
dum.py:18: note:          def method(self, a: int) -> int
dum.py:18: note:          @overload
dum.py:18: note:          def method(self, a: str) -> str
dum.py:18: note:      Subclass:
dum.py:18: note:          def method(self, a: int | str) -> int | str

Your Environment

• Mypy version used: 1.5.1
• Python version used: 3.11

(Probably) related issues:

• False positive: signature incompatible with supertype #13106
  • Opened a new issue since that was closed, and the conversation was on more complex cases
• False positive: signature incompatible with supertype if subtype has overloads #14725
  • The reversed(?) version of this issue
• Non-applicable overloads should not be requested in subclasses #13591
  • Seems to be fixed

[JelleZijlstra]

This is not a false positive. With the superclass signature, you're guaranteed to get an int back if you pass an int. With the subclass signature, you may get a str back instead. Therefore, the subclass signature is incompatible and mypy is right to show an error.

[SubaruArai]

@JelleZijlstra Is this what happens internally? (At least philosophically)

1. parent method gets annotated as overloaded
2. child method created (parent method annotations are ignored - for if you want to change the type hints)
3. mypy detects inconsistency between parent and child

[JelleZijlstra]

Correct.

[SubaruArai]

Ok, thanks!

[JelleZijlstra]

#14725 is a false positive, because there the subclass signature is compatible.

[SubaruArai]

Yeah, sorry misread it. Edited the comment.