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

Bắt đầu bằng cách chạy reproducer detect.py được cung cấp với các phiên bản mypy đã báo cáo và kiểm tra cách suy luận Callable và TypeVar xử lý các đối số lambda và is_even. Theo dõi hành vi kiểm tra kiểu liên quan và bổ sung phạm vi kiểm thử hồi quy khi thích hợp; được xem là hoàn tất khi ví dụ được kiểm tra kiểu mà không có hai lỗi đã báo cáo.