inspect.isfunction and inspect.ismethod

[mristin]

Bug Report

I use an union between a callable and a class:

# example.py

import inspect
from typing import Union, Callable, Type


def some_func(
        error: Union[Callable[..., BaseException], Type[BaseException]]
)->None:
    if (inspect.isfunction(error) or inspect.ismethod(error)):
        reveal_type(error)
    else:
        reveal_type(error)

Mypy does not infer that the type is Callable based on inspect.isfunction and inspect.ismethod, but still assumes the union:

example.py:9: note: Revealed type is 'Union[def (*Any, **Any) -> builtins.BaseException, Type[builtins.BaseException]]'
example.py:11: note: Revealed type is 'Union[def (*Any, **Any) -> builtins.BaseException, Type[builtins.BaseException]]'

To Reproduce

Execute the following command:

mypy example.py

Your Environment

• Mypy version used: 0.812

[mristin]

(I am not sure if this is a bug or a feature request, please change as you see fit.)

[JelleZijlstra]

This should be fixable in typeshed once we have support for PEP 647 (https://www.python.org/dev/peps/pep-0647/). Mypy could also special-case these functions directly but that might be overkill.

[mristin]

@JelleZijlstra thanks for considering the issue. In fact, I think that mypy should handle inspect.is* methods directly as this seems a canonical way to check whether an object is a callable, a coroutine etc. at runtime.

Otherwise, it would be great if mypy documentation explicitly stated how the user is expected to check for "is a callable" property. (There is no isinstance(obj, Callable) as far as I am aware.)

Edit: typo

[JelleZijlstra]

We support using callable() (as of #2627).

[AlexWaygood]

Hmm, well, TypeGuard is now supported and the relevant changes to typeshed have been made, but there still seem to be some problems on mypy's end:

import inspect
from typing import Union, Callable, Type


def some_func(
        error: Union[Callable[..., BaseException], Type[BaseException]]
)->None:
    if (inspect.isfunction(error) or inspect.ismethod(error)):
        reveal_type(error)  # Revealed type is "<nothing>"
    else:
        reveal_type(error)  # Revealed type is "Union[def (*Any, **Any) -> builtins.BaseException, Type[builtins.BaseException]]"

[erictraut]

It looks like this is working as expected with the latest version of mypy.

The first revealed type is now:

Revealed type is "Union[types.FunctionType, types.MethodType]"