Reporting "too many arguments" to __init__ for class which takes *args

[anentropic]

Trying to add hints to this:

class ValidationError(Exception):

    def __init__(self, message: str, log_level: int=logging.ERROR, *args, **kwargs) -> None:
        self.message = message
        self.log_level = log_level
        super().__init__(message, log_level, *args, **kwargs)

gives:

error: Too many arguments for "__init__" of "BaseException"

Well, Exception.__init__ supposedly takes *args, **kwargs so how can this ever have "too many arguments"?

If I change my code to:

class ValidationError(Exception):

    def __init__(self, message: str, log_level: int=logging.ERROR) -> None:
        self.message = message
        self.log_level = log_level
        super().__init__(message, log_level)

then no error reported.

I'm actually happy with this change to my code. But does it suggest an issue with mypy?

This also works:

class ValidationError(Exception):

    def __init__(self, message: str, log_level: int=logging.ERROR, whatever: str='WTF') -> None:
        self.message = message
        self.log_level = log_level
        super().__init__(message, log_level, whatever)

So it seems the issue is not with any specific number of arguments, but of mypy not understanding that *args means 'any number'?

[JelleZijlstra]

This is a typeshed issue. The problem is that BaseException.__init__ in stdlib/3/builtins.pyi is defined as def __init__(self, *args: object) -> None: .... This means it takes arbitrary args, but not arbitrary kwargs, and your code passes **kwargs. The fix is obvious; could you submit a PR or issue to https://github.com/python/typeshed to fix it?

[anentropic]

@JelleZijlstra thanks, have opened a PR against typeshed

[Callek]

For anyone who find this in a search - BaseException.init doesn't take keyword args and this was reverted in python/typeshed#2348