Safe way for implementing singledispatch

dispatch.py

from functools import singledispatch
from dataclasses import dataclass
from typing import Union, get_args

@dataclass
class Foo:
    id: str
    name: str


Command = Union[Foo, str]


@singledispatch
def dispatch(arg: Command, /):
    raise NotImplementedError


@dispatch.register
def _(arg: Foo, /):
    print(arg)


@dispatch.register
def _(arg: str, /):
    print(arg)


assert len(get_args(Command)) + 1 == len(dispatch.registry)

dispatch(Foo("id", "name"))
dispatch("ok")