Standard library map on bound function

Bắt đầu với việc tái hiện trong test.py đã được báo cáo, tập trung vào sự tương tác giữa returns.pointfree.bind, ResultE và map tích hợp sẵn của Python. So sánh các kiểu được mypy suy luận với vòng lặp for đang hoạt động và các phương án g tường minh; hoàn tất có nghĩa là ví dụ map(bind(g), map(f, range(3))) ban đầu kiểm tra kiểu mà không có lỗi.

Bug report

Mypy does not appear to correctly handle the standard library map function over an iterable of containers that returns an iterable of containers, when the function being mapped over the data has had returns.pointfree.bind applied to it. The same code when used without map (by explicit use of a for-loop) or a bind (by explicitly handling a container input) will not result in an error.

What's wrong

Code to reproduce issue

from typing import Iterable

from returns.pointfree import bind
from returns.result import ResultE
from returns.result import safe


@safe
def f(x: int) -> str:
    return str(x)


@safe
def g(x: str) -> int:
    return int(x)


def h(xs: Iterable[ResultE[int]]) -> None:
    for x in xs:
        print(x.unwrap())


if __name__ == "__main__":
    h(map(bind(g), map(f, range(3))))

Mypy output

$ mypy test.py
test.py:24:11: error: Argument 1 to "map" has incompatible type "Kinded[Callable[[KindN[Result[Any, Any], str, Exception, NoReturn]], KindN[Result[Any, Any], int, Exception, NoReturn]]]"; expected "Callable[[Result[str, Exception]], Res
ult[int, Exception]]"  [arg-type]
test.py:24:11: note: "Kinded[Callable[[KindN[Result[Any, Any], str, Exception, NoReturn]], KindN[Result[Any, Any], int, Exception, NoReturn]]].__call__" has type "Callable[[KindN[Result[Any, Any], str, Exception, NoReturn]], KindN[Resul
t[Any, Any], int, Exception, NoReturn]]"
Found 1 error in 1 file (checked 1 source file)

Python output

$ python test.py
0
1
2

How it should be

When the h function is replaced with a for-loop in __main__ no issues are reported by Mypy and the code executes correctly:

if __name__ == "__main__":
    for x in map(f, range(3)):
        print(x.bind(g).unwrap())

Can also fix the issue by swapping out the g function:

def g(x: ResultE[str]) -> ResultE[int]:
    return x.map(int)

<snip>

if __name__ == "__main__":
    h(map(g, map(f, range(3))))

System information

• python version: 3.8.6
• returns version: 0.15.0
• mypy version: 0.800 (also observed in v0.782 due to classess library dependency)