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False positive when using Self as the return type with multiple base classes #17704
Description
Bug Report
If you try to derive from multiple base classes that both define the same function returning Self, mypy incorrectly warns that the definitions are incompatible.
To Reproduce
# https://mypy-play.net/?mypy=latest&python=3.12&gist=e5d3734df862e8f3ada5c11c076cae57
# main.py
from typing import Self
class MyBase1:
def foo(self) -> Self:
return self
class MyBase2:
def foo(self) -> Self:
return self
class MyDerived(MyBase1, MyBase2):
pass
MyBase1().foo() # Should be Valid. Has type MyBase1
MyBase1().foo() # Should be Valid. Has type MyBase2
MyDerived().foo() # Should be Valid. Has type MyDerivedExpected Behavior
Shouldn't report any errors. In the context of the line class MyDerived(MyBase1, MyBase2): both MyBase1 and MyBase2 returns Self aka MyDerived
Actual Behavior
$ mypy main.py
main.py:13: error: Definition of "foo" in base class "MyBase1" is incompatible with definition in base class "MyBase2" [misc]
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: mypy 1.11.1 (compiled: yes)
- Mypy command-line flags:
- Mypy configuration options from
mypy.ini(and other config files): - Python version used: 3.12
Activity
Cnoor0171 commentedon Aug 22, 2024
A similar problem if the methods are classmethods
Interestingly, mypy is also able to derive the correct type of
MyDerived.foo()orMyDerived().foo()if you doreveal_typeon them.sterliakov commentedon Jan 15, 2025
Missed this ticket - also resolved by #18465 and passes on current master.