Type error when implementing additional responses

[ryanditjia]

Following the example from the additional responses guide:

class Message(BaseModel):
    message: str


responses = {
    401: {"model": Message}
}


@router.put("/me/password", responses=responses, status_code=status.HTTP_204_NO_CONTENT)

I’m getting this mypy error on responses argument:

Argument "responses" to "put" of "APIRouter" has incompatible type "Dict[int, Dict[str, Type[Message]]]"; expected "Optional[Dict[Union[int, str], Dict[str, Any]]]"

When I change the argument to responses={**responses}, the error is still there, albeit a little bit different:

List item 0 has incompatible type "Dict[int, Dict[str, Type[Message]]]"; expected "Mapping[Union[int, str], Dict[str, Any]]"

Does anyone know why this is happening?

[vrodochenko]

I would assume that mypy cannot derive the type of your dictionary the way you want it to, which leads to this obscure error. Consider adding an annotation:

from typing import Dict

responses: Dict = {
    401: {"model": Message}
}

to make things pass the validation.

Also you can go through mypy issues (e.g this one) to learn more.

[ryanditjia]

Thanks so much, your answer worked.

[tiangolo]

Thanks for the help @vrodochenko ! 🍰

And thanks for coming back to close the issue @ryanditjia ☕

Sorry for the long delay! 🙈 I wanted to personally address each issue/PR and they piled up through time, but now I'm checking each one in order.