Type issues with Callables

• Are you reporting a bug, or opening a feature request?
  bug

• Please insert below the code you are checking with mypy

from typing import Optional, Iterable, TypeVar, Callable

T = TypeVar('T')


def is_even(n: int) -> bool:
    return n % 2 == 0


# equivalent to https://ruby-doc.org/core-2.5.0/Enumerable.html#method-i-detect
def detect(function: Callable[[T], bool],
           iterable: Iterable[T]) -> Optional[T]:
    for element in iterable:
        if function(element):
            return element
    return None


numbers = [1, 2, 3, 4, 5]

# using a lambda
print(detect(lambda n: n % 2 == 0, numbers))

# using a function
print(detect(is_even, numbers))

• What is the actual behavior/output?

$ mypy detect.py 
detect.py:22: error: Unsupported operand types for % ("object" and "int")
detect.py:25: error: Argument 1 to "detect" has incompatible type "Callable[[int], bool]"; expected "Callable[[object], bool]"
Found 2 errors in 1 file (checked 1 source file)

• What is the behavior/output you expect?
  I was expecting the types to be inferred and the above code to typecheck.

• What are the versions of mypy and Python you are using?

$ mypy --version
mypy 0.770
$ python --version
Python 3.7.7

• Do you see the same issue after installing mypy from Git master?
  yes

$ mypy detect.py
detect.py:22: error: Unsupported operand types for % ("object" and "int")
detect.py:25: error: Argument 1 to "detect" has incompatible type "Callable[[int], bool]"; expected "Callable[[object], bool]"
Found 2 errors in 1 file (checked 1 source file)
$ mypy --version
mypy 0.770+dev.22c67daac7d2b28f33d4e9c7bee4f1a06e61a3e5

• What are the mypy flags you are using? (For example --strict-optional)
  None.

• If mypy crashed with a traceback, please paste the full traceback below.
  It didn't crash

Commencez par exécuter le reproducteur detect.py fourni avec les versions de mypy signalées et examinez comment l’inférence de Callable et TypeVar traite les arguments lambda et is_even. Suivez le comportement pertinent de la vérification des types et ajoutez une couverture de régression lorsque cela est approprié ; le travail est considéré comme terminé lorsque l’exemple est vérifié par le système de types sans les deux erreurs signalées.