to summarizesubscriber objects can register and unregister with the publisher object so whenever an eventthat drives the publisher' notification methodoccursthe publisher notifies the subscriber objects the notifications would only be passed to the objects that are registered with the subject at the time of occurrence of the event sample python implementation example description let' take the example of techforum on which technical posts are published by different users the users might subscribe to receive notifications when any of the other users publishes new post to see this in the light of objectswe could have _techforumobject and we can have another list of objects called _userobjects that are registered to the _techforumobjectthat can observe for any new posts on the _techforumalong with the new post notificationthe title of the post is sent similar analogy could be drawn in terms of job agency and job seekers/employers this could be an extension where employers and job seekers subscribe to two different kinds of notification via common subject (job agencyjob seekers would be looking for relevant job notifications and employers would be looking for new job seeker registration fitting job profile python code class publisherdef __init__(self)#make it uninheritable pass def register(self)#override pass def unregister(self)#override pass def notifyall(self)#override pass class techforum(publisher)def __init__(self)self _listofusers [self postname none www testingperspective com