Too many arguments / Invalid self argument when referencing callable attribute of an object.

[mkielar]

Bug Report

To Reproduce

This code:

import dataclasses as dc
from enum import Enum
from typing import cast, Any, Callable, Dict, List


class ScalingDirection(Enum):
    SCALE_UP = 'up'
    SCALE_DOWN = 'down'


@dc.dataclass
class InstanceScalingStatus:
    label: str
    scaling_check: Callable[[ScalingDirection], bool]
    is_scaling_finished: bool = False


def _check_scaling_states(scaling_states: Dict[str, InstanceScalingStatus],
                          scaling_direction: ScalingDirection) -> bool:
    
    for name, scaling_state in scaling_states.items():
        if scaling_state.scaling_check(scaling_direction):
            scaling_state.is_scaling_finished = True

    not_yet_scaled: List[str] = [state.label for state in scaling_states.values() if not state.is_scaling_finished]
    if len(not_yet_scaled) > 0:
        return False

    return True    

Expected Behavior

The scaling_state.scaling_check(scaling_direction) is not a function call on an object. There's no self and the Callable clearly states it only takes a single argument. It's a de-reference of a attribute that points to a callable, and call to that callable. It works, no other linter we use complains about this syntax. I belive mypy shouldn't either.

Actual Behavior

Fails with:

→ mypy --version
mypy 0.800
→ mypy test2.py
test2.py:22: error: Invalid self argument "InstanceScalingStatus" to attribute function "scaling_check" with type "Callable[[ScalingDirection], bool]"
test2.py:22: error: Too many arguments
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.800
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.8.3
• Operating system and version: Windows 10 / WSL 1 / FedoraRemix 31

[mkielar]

if getattr(scaling_state, 'scaling_check')(scaling_direction):
            scaling_state.is_scaling_finished = True

This fooled mypy into being silent. Not sure what's uglier though, doing this, or inline ignores.

[Akuli]

It no longer errors on master:

(env310) akuli@akuli-desktop:~/mypy$ python3 -m mypy a.py
Success: no issues found in 1 source file

(env310) akuli@akuli-desktop:~/mypy$ cat a.py
import dataclasses as dc
from enum import Enum
from typing import cast, Any, Callable, Dict, List


class ScalingDirection(Enum):
    SCALE_UP = 'up'
    SCALE_DOWN = 'down'


@dc.dataclass
class InstanceScalingStatus:
    label: str
    scaling_check: Callable[[ScalingDirection], bool]
    is_scaling_finished: bool = False


def _check_scaling_states(scaling_states: Dict[str, InstanceScalingStatus],
                          scaling_direction: ScalingDirection) -> bool:
    
    for name, scaling_state in scaling_states.items():
        if scaling_state.scaling_check(scaling_direction):
            scaling_state.is_scaling_finished = True

    not_yet_scaled: List[str] = [state.label for state in scaling_states.values() if not state.is_scaling_finished]
    if len(not_yet_scaled) > 0:
        return False

    return True    

[NeilGirdhar]

@JelleZijlstra Should this be closed?