from collections.abc import Callable
from typing import Protocol

class C(Protocol):
    def __call__(self, a: int, b: str, c: bytes = b'', /) -> None: ...

def foo(c: C) -> None: ...


f: Callable[[int, str, bytes], None]
c: C

# error: Incompatible types in assignment (expression has type "Callable[[int, str, bytes], None]", variable has type "C")
# note: "C.__call__" has type "Callable[[int, str, DefaultArg(bytes)], None]"
c = f

# error: Argument 1 to "foo" has incompatible type "Callable[[int, str, bytes], None]"; expected "C"
foo(f)