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Returning optional union from method complains about got "object" #12823
Description
Bug Report
Mypy thinks my method returns "object" which is not right.
To Reproduce
Run Mypy on this file:
from typing import Optional
class Cat:
pass
class Dog:
pass
class MyClass:
def __init__(self) -> None:
self.pet: Optional[Dog | Cat] = None
def get_pet(self) -> Optional[Dog | Cat]:
if input() == 'yes':
self.pet = Cat()
else:
self.pet = Dog()
return self.pet # (incorrect Mypy error on this line!)Expected Behavior
This should have no errors.
Actual Behavior
It yields:
error: Incompatible return value type (got "object", expected "Union[Dog, Cat, None]")
Your Environment
- Mypy version used: v0.950
- Mypy command-line flags: none
- Mypy configuration options: none
- Python version used: 3.10.4
- Operating system and version: Ubuntu 20.04
Activity
erictraut commentedon May 20, 2022
Looks like another case where a false positive results from using a join operation rather than a union.
hauntsaninja commentedon May 22, 2022
Note the following works:
Looks like we're losing the type context of the instance variable.
sterliakov commentedon Mar 28, 2025
Fixed in #18538 and passes on current master.