Not None checks ignored when passing to a lambda

[ltworf]

from typing import *

def f(p: Optional[str]) -> Callable[[str], bool]:
    assert p
    if p is None:
        raise Exception('asd')
    return lambda a: p.startswith(a)

This doesn't pass, despite the 2 checks to make sure that p is indeed a string.

[ltworf]

It seems to work if instead of the lamda I use functools.partial

[kaste]

This is a dupe of #4297

Note that most of the time lambda gives you more type safety than partial. Of course, partial gives you more programming safety. But, using it here you just mute the mypy error.

[JelleZijlstra]

Closing as a duplicate.