from typing import Union


class Foobar:
    def __init__(self, x: Union[int, str]):
        self._x = self.makestr(x)

    def makestr(self, x: Union[int, str]) -> str:
        if isinstance(x, int):
            return str(x)
        elif isinstance(x, str):
            return x
        else:
            raise Exception("invalid type")

    @property
    def x(self) -> str:
        return self._x

    @x.setter
    def x(self, x: Union[int, str]) -> None:
        self._x = self.makestr(x)


fb = Foobar("abc")
fb.x = 3