Summary

This chapter discussed several common design patterns in detail, with examples, UML diagrams, and a discussion of the differences between Python and statically typed object-oriented languages. The Decorator pattern is often implemented using Python's more generic decorator syntax. The Observer pattern is a useful way to decouple events from actions taken on those events. The Strategy pattern allows different algorithms to be chosen to accomplish the same task. The Command pattern helps us design active classes that share a common interface but carry out distinct actions. The State pattern looks similar to the Strategy pattern but is used instead to represent systems that can move between different states using well-defined actions. The Singleton pattern, popular in some statically typed languages, is almost always an anti-pattern in Python.

In the next chapter, we'll wrap up our discussion of design patterns.