A super simples result monad approach

result_monad.py

from typing import Generic, TypeVar, Union, Optional

T = TypeVar("T")
E = TypeVar("E")


class _Ok(Generic[T]):
    def __init__(self, value: Optional[T] = None) -> None:
        self.value = value
        self.is_ok = True


class _Err(Generic[E]):
    def __init__(self, value: E) -> None:
        self.value = value
        self.is_ok = False


Result = Union[_Ok[T], _Err[E]]


def Ok(value: Optional[T] = None) -> _Ok[T]:
    return _Ok(value)


def Err(value: E) -> _Err[E]:
    return _Err(value)