from __future__ import annotations


class A:
    def __init__(self, value: int):
        self.value = value

    def __add__(self, other: int) -> int:
        if not isinstance(other, int):
            return NotImplemented
        return self.value + other


class B:
    def __init__(self, value: int):
        self.value = value

    def __add__(self, other: A) -> B:
        if not isinstance(other, A):
            return NotImplemented
        return self.value + other.value

    def __radd__(self, other: A) -> int:
        if not isinstance(other, A):
            return NotImplemented
        return self.value + other.value


if __name__ == "__main__":
    a = A(5)
    b = B(10)

    print(a + 3)  # print 8
    print(a + b)  # print 15
    print(a + "test")  # raises TypeError
# Traceback (most recent call last):
#   File "test.py", line 35, in <module>
#     print(a + "test")  # raises TypeError
#           ~~^~~~~~~~
# TypeError: unsupported operand type(s) for +: 'A' and 'str'