如何做一个轻量级的只能订阅一次的`Replay`运算符？

class Replay:
    def __init__(self):
        self.subscribers = []
        self.cache = []

    def subscribe(self, subscriber):
        if self.cache:
            for data in self.cache:
                subscriber(data)
            self.cache = []
        else:
            self.subscribers.append(subscriber)

    def next(self, data):
        self.cache.append(data)
        for subscriber in self.subscribers:
            subscriber(data)

    def unsubscribe(self, subscriber):
        self.subscribers.remove(subscriber)