mypy-guide-generics-5.py

from typing import Dict, TypeVar, Union

T = TypeVar('T')
MyOptional = Union[T, None]

def get_unicorn(d: Dict[str, int]) -> MyOptional[int]:
    return d.get('unicorn')

d = {'x': 5}
unicorn = get_unicorn(d)

reveal_type(unicorn)  # Union[int, None]
print(unicorn)        # None