10.5. Special

10.5.1. Optional

from typing import Optional


def non_zero(number: int) -> Optional[int]:
    if not number:
        return None
    else:
        return number

10.5.2. Union

from typing import Union


def round(number: Union[int, float]) -> int:
    return int(number)

from typing import Union, Sequence


def fire_employees(e: Union[Employee, Sequence[Employee]]) -> None:
    print(employee)

10.5.3. Any

from typing import Any


def echo(value: Any) -> None:
    print(value)

10.5.4. Literal

• Since Python 3.8: PEP 586 -- Literal Types

from typing import Literal

def accepts_only_four(x: Literal[4]) -> None:
    pass

accepts_only_four(4)   # OK
accepts_only_four(19)  # Rejected

from typing import Literal, overload


@overload
def open(path: str,
         mode: Literal["r", "w", "a", "x", "r+", "w+", "a+", "x+"],
         ) -> IO[str]: ...

@overload
def open(path: str,
         mode: Literal["rb", "wb", "ab", "xb", "r+b", "w+b", "a+b", "x+b"],
         ) -> IO[bytes]: ...