observer pattern mentioned couplingso let me clarify what is meant when we talk about coupling generallywhen we talk about the level of coupling between objectswe refer to the degree of knowledge that one object needs with regard to other objects that it interacts with the more loosely objects are coupledthe less knowledge they have about each otherand the more flexible the object-oriented system is loosely coupled systems have fewer interdependencies between objects and as such are easier to update and maintain by decreasing the coupling between objectsyou further reduce the risk that changing something in one part of the code will have unintended consequences in some other part of the code since objects do not rely on each otherunit testing and troubleshooting become easier to do other good places to use the observer pattern include the traditional model-viewcontroller design patternwhich you will encounter later in the bookas well as textual description of data that needs to be updated whenever the underlying data changes as rulewhenever you have publish-subscribe relationship between single object (the observableand set of observersyou have good candidate for the observer pattern some other examples of this type of architecture are the many different types of feeds you find onlinelike newsfeedsatomrssand podcasts with all of thesethe publisher does not care who the subscribers areand thus you have natural separation of concern the observer pattern will make it easy to add or remove subscribers at runtime by increasing the level of decoupling between the subscribers and the publisher nowlet' use the pythonic implementation of the observer pattern to implement our tracking system from the beginning of the note how easy it is to add new classes to the code and how clean the processes of updating and changing any of the existing classes are class task(object)def __init__(selfuser_type)self observers set(self user user self _type _type def register(selfobserver)self observers add(observer