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main.py

from __future__ import annotations

from enum import IntEnum
from typing import Protocol, Self, cast, reveal_type

class SupportsAdd(Protocol):
    def __add__(self, other: Self, /) -> Self: ...

def add_one[T: SupportsAdd](value: T) -> T:
    match value:
        case int():
            return cast("T", value + 1)
        case str():
            return cast("T", value + " and one more")
        case _:
            raise TypeError()

class Options(IntEnum):
    A = 1
    B = 2
    C = 3

def test(i: int, s: str, i_s: int | str, o: Options) -> None:
    reveal_type(add_one(i))
    reveal_type(add_one(s))
    reveal_type(add_one(i_s))
    reveal_type(add_one(o))
    reveal_type(add_one(int(o)))