Learning Python Design Patterns - Second Edition

A simple example of the State design pattern

Let's understand all three participants with a simple example. Say, we want to implement a TV remote with a simple button to perform on/off actions. If the TV is on, the remote button will switch off the TV and vice versa. In this case, the State interface will define the method (say, doThis()) to perform actions such as switching on/off the TV. We also need to define ConcreteClass for different states. In this example, we have two major states, StartState and StopState, which indicate when the TV is switched on and the state in which the TV is switched off, respectively.

For this scenario, the TVContext class will implement the State interface and keep a reference to the current state. Based on the ...