design pattern quick reference class dispatcher(object)def __init__(self)self topic_subscribers dict(def subscribe(selfsubscribertopic)self topic_subscribers setdefault(topicset()add(subscriberdef unsubscribe(selfsubscribertopic)self topic_subscribers setdefault(topicset()discard(subscriberdef unsubscribe_all(selftopic)self subscribers self topic_subscribers[topicset(def send(selfmessage)for subscriber in self topic_subscribers[message topic]subscriber process(messagefinal words well doneyou have learned many useful patterns hope that you will continue to practice and become better programmer every day thank you for going on this journey with me goodbye and good luck