from typing import Callable, Optional

# ✅ type-checks fine

def _fn0(fn: Callable[[int], bool], s: int) -> bool:

return fn(s)

def fn0(s: int) -> bool:

return True

# ❌ TypeCheckError: argument "fn" (function) has too many mandatory positional arguments in its declaration; expected 0 but 1 mandatory positional argument(s) declared

def _fn1(fn: Callable[[Optional[int]], bool], s: Optional[int]) -> bool:

return fn(s)

def fn1(s: Optional[int]) -> bool:

return True

def test_fn0():

"""Passing a Callable (``fn0``) works, as long as its arguments are not ``Optional``."""

_fn0(fn0, 123) # ✅ OK

def test_fn1():

"""Functions that take optional arguments are not type-checked properly"""

_fn1(fn1, 123) # ❌ TypeCheckError: argument "fn" (function) has too many mandatory positional arguments in its declaration; expected 0 but 1 mandatory positional argument(s) declared