Suggest using Protocol when user tries to use keyword args with Callable

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#1,655 10 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start by reproducing the two examples in sample_python.py and inspect how mypy handles Callable annotations and keyword arguments. Review the issue's proposed Protocol direction and establish expected behavior for both examples; done means the agreed behavior is implemented and covered by tests for these cases.

Written by the indexing model from the issue text.

Description

false-positive priority-1-normal topic-usability

If I define a passed in function using the Callable syntax, mypy complains if I then call a keyword argument on that function. This is makes writing things like decorators problematic

Sample code:

from typing import Callable

def test_func(a, b, c=0, d=0):
    # type: (int, int, int, int) -> int
    return a + b + c + d

def check_func(method):
    # type: (Callable[[int, int, int], int]) -> int
    return method(1, 2, d=5)

print(check_func(test_func))

$ mypy sample_python.py
sample_python.py: note: In function "check_func":
sample_python.py:9: error: Unexpected keyword argument "d"

As an aside here, I the following function code also raises mypy errors:

from typing import Callable

def test_func(a, b, *, c, d):
    # type: (int, int, int, int) -> int
    return a + b + c + d

def check_func(method):
    # type: (Callable[[int, int, int, int], int]) -> int
    return method(1, 2, c=5, d=10)

print(check_func(test_func))
Dominant language
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