Python Observer pattern

The Subject is the entity that the Observer watches. The Subject is single entity and the Observers can be more than one . The Subject has the List observers, but the Observer will have the Subject. Any change in the Subject will be notified to all the observers that the Subject stores in the form of a list.

The Observer pattern offers a subscription model in which objects subscribe to an event and get notified when the event occurs . This pattern is the cornerstone of event driven programming, including JavaScript. The Observer pattern facilitates good object-oriented design and promotes loose coupling.

Observer pattern is used when there is one-to-many relationship between objects such as if one object is modified , its depenedent objects are to be notified automatically. Observer pattern falls under behavioral pattern category.

Interface Observer public interface Observer. A class can implement the Observer interface when it wants to be informed of changes in observable objects .

The Observer Pattern is the foundation of the Model View Controller (MVC) pattern, in which a view is updated automatically whenever the model’s state changes . In the . NET Framework, delegates with events are an implementation of the Observer pattern.

The observer pattern is a software design pattern in which an object, named the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.