Redis Pub/Sub Channel Subscribe Mock in Python

class MockRedisPubSub:
    def __init__(self):
        self.channels = {}

    def subscribe(self, channel):
        if channel not in self.channels:
            self.channels[channel] = []
        return self.channels[channel]

    def publish(self, channel, message):
        if channel in self.channels:
            for handler in self.channels[channel]:
                handler(message)
            return len(self.channels[channel])
        return 0

    def unsubscribe(self, channel, handler=None):
        if channel in self.channels:
            if handler is None:
                self.channels[channel] = []
            else:
                self.channels[channel].remove(handler)


if __name__ == "__main__":
    mock = MockRedisPubSub()
    received = []

    mock.subscribe("news").append(lambda msg: received.append(f"news: {msg}"))
    mock.subscribe("sports").append(lambda msg: received.append(f"sports: {msg}"))

    mock.publish("news", "breaking story")
    mock.publish("sports", "game result")
    mock.publish("unknown", "nobody hears this")

    for item in received:
        print(item)