from typing import Callable, TypeVar, Generic, TypeGuard, Any, List, Optional, overload

_T = TypeVar('_T')

class filter(Generic[_T]):
    @overload
    def __init__(self, __function: Callable[[object], TypeGuard[_T]]) -> None: ...
    @overload
    def __init__(self, __function: Callable[[_T], Any]) -> None: ...

# Demo:

a: List[Optional[int]]
def is_int_typeguard(a: object) -> TypeGuard[int]: pass
def returns_bool(a: object) -> bool: pass

# Ok:
reveal_type(filter(is_int_typeguard))  # N: Revealed type is "ex.filter[builtins.int*]"

# Not ok:
reveal_type(filter(returns_bool))  # N: Revealed type is "ex.filter[builtins.bool*]"
# Expected: Revealed type is "ex.filter[builtins.object*]"