Inadvisable adventures with the match statement

gcd.py

import operator


class Bigger(type):
    def __new__(cls, op):
        self = super().__new__(cls, "spam", (), {})
        self.op = op
        return self

    def __instancecheck__(self, instance):
        match instance:
            case (a, b):
                return self.op(a, b)
        return False


a_is_bigger = Bigger(operator.gt)
b_is_bigger = Bigger(operator.lt)


def gcd(a: int, b: int) -> int:
    while True:
        match (a, b):
            case (r, 0) | (0, r):
                return r
            case a_is_bigger():
                a %= b
            case b_is_bigger():
                b %= a
            case _:
                return a