class SimplePubSub:
    def subscribe(self, event, listener):
        pass
    def unsubscribe(self, event, listener):
        pass
    def publish(self, event, data):
        pass

# 创建 PubSub 实例
pubSub = SimplePubSub()

def subscriber1(data):
    print(f'Subscriber 1 received: {data}')

def subscriber2(data):
    print(f'Subscriber 2 received: {data}')

# 订阅事件
pubSub.subscribe('event1', subscriber1)
pubSub.subscribe('event1', subscriber2)

# 发布事件
pubSub.publish('event1', 'Hello, World!')

# 取消订阅
pubSub.unsubscribe('event1', subscriber1)

# 发布事件
pubSub.publish('event1', 'Hello again!')

# 输出应该是如下的样式

# Subscriber 1 received: Hello, World!
# Subscriber 2 received: Hello, World!
# Subscriber 2 received: Hello again!