Mastering Python Design Patterns

Summary

In this chapter, we covered the Chain of Responsibility design pattern. This pattern is useful to model requests / handle events when the number and type of handlers isn't known in advance. Examples of systems that fit well with Chain of Responsibility are event-based systems, purchase systems, and shipping systems.

In the Chain Of Responsibility pattern, the sender has direct access to the first node of a chain. If the request cannot be satisfied by the first node, it forwards to the next node. This continues until either the request is satisfied by a node or the whole chain is traversed. This design is used to achieve loose coupling between the sender and the receiver(s).

ATMs are an example of Chain Of Responsibility. The single slot ...