Learning Python Design Patterns - Second Edition

Understanding the Command design pattern

The Command pattern works with the following terms—Command, Receiver, Invoker, and Client:

• A Command object knows about the Receiver objects and invokes a method of the Receiver object.
• Values for parameters of the receiver method are stored in the Command object
• The invoker knows how to execute a command
• The client creates a Command object and sets its receiver

The main intentions of the Command pattern are as follows:

• Encapsulating a request as an object
• Allowing the parameterization of clients with different requests
• Allowing to save the requests in a queue (we will talk about this later in the chapter)
• Providing an object-oriented callback

The Command pattern can be used in the following multiple scenarios: