Mastering Python Design Patterns - Second Edition

The State Pattern

In the previous chapter, we covered the Observer pattern, which is useful in a program to notify other objects when the state of a given object changes. Let's continue discovering those patterns proposed by the Gang of Four.

Object-oriented programming (OOP) focuses on maintaining the states of objects that interact with each other. A very handy tool to model state transitions when solving many problems is known as a finite-state machine (commonly called a state machine).

What's a state machine? A state machine is an abstract machine that has two key components, that is, states and transitions. A state is the current (active) status of a system. For example, if we have a radio receiver, two possible states for it are to ...