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enumerate causes incompatible type mypy error #11934
Description
Bug Report
When using the enumerate function mypy seems to generalise the output to object instead of respecting the type of the input
To Reproduce
from typing import Union
def process(actions: Union[list[str], list[int]]) -> None:
for pos, action in enumerate(actions):
act(action)
def act(action: Union[str, int]) -> None:
print(action)
Expected Behavior
Mypy raises no errors
Actual Behavior
Mypy raises the following error: Argument 1 to "act" has incompatible type "object"; expected "Union[str, int]"
Its worth noting that the same code without using enumerate does not raise this error:
from typing import Union
def process(actions: Union[list[str], list[int]]) -> None:
for action in actions:
act(action)
def act(action: Union[str, int]) -> None:
print(action)
Your Environment
- Mypy version used: 0.921
- Python version used: 0.9
Activity
sobolevn commentedon Jan 9, 2022
You can try this (if you are using
python>=3.9):But, I agree that automatically infering
str | inthere can be a good feature. But, it is really hard to do 🙂erictraut commentedon Jan 9, 2022
This is yet another case where mypy's choice to use join rather than union causes problems. Pyright uses only unions, never joins, so it produces the expected result in this case.
Has there been any serious discussion of changing mypy's behavior to use unions instead of joins? I can't think of any case where joins are preferable, and there are many cases where unions are better because they retain more detailed type information.
sobolevn commentedon Jan 9, 2022
CC @JukkaL
AlexWaygood commentedon Mar 29, 2022
Closing as a duplicate of #8586