In the previous chapter, we started with a brief introduction to Proxy and went ahead to discuss the Proxy design pattern. We understood the concept of the Proxy pattern with a UML diagram and also learned how it's applied in the real world with the help of Python implementations. You learned about the ups and downs of the Proxy pattern with the FAQ section.
In this chapter, we will talk about the third type of design pattern—the behavioral design pattern. We will be introduced to the Observer design pattern, which falls under the hood of Behavioral patterns. We will discuss how the Observer design pattern is used in software application development. We will work with a sample use case and implement it in Python v3.5.
In this chapter, we will cover the following topics in brief:
- An introduction to behavioral design patterns
- The Observer pattern and its UML diagram
- A real-world use case with the Python v3.5 code implementation
- The power of loose coupling
- Frequently asked questions
At the end of the chapter, we will summarize the entire discussion—consider this a takeaway.
In the previous chapters of the book, you learned about creational patterns (Singleton) and structural patterns (Façade). In this section, we will get a brief idea of Behavioral patterns.
Creational patterns work on the basis of how objects can be created. They isolate the details of object creation. Code is independent of the type of object to be created. Structural patterns design the structure of objects and classes so that they can work together to achieve larger results. Their main focus is on simplifying the structure and identifying relationships between classes and objects.
Behavioral patterns, as the name suggests, focus on the responsibilities that an object has. They deal with the interaction among objects to achieve larger functionality. Behavioral patterns suggest that while the objects should be able to interact with each other, they should still be loosely coupled. We will learn about the principle of loose coupling later in this chapter.
The Observer design pattern is one of the simplest Behavioral patterns. So, let's gear up and understand more about them.