Mastering Python Design Patterns

Implementation

There are many ways to implement Chain of Responsibility in Python, but my favorite implementation is the one by Vespe Savikko [j.mp/savviko]. Vespe's implementation uses dynamic dispatching in a Pythonic style to handle requests [j.mp/ddispatch].

Let's implement a simple event-based system using Vespe's implementation as a guide. The following is the UML class diagram of the system:

The Event class describes an event. We'll keep it simple, so in our case an event has only name:

class Event: 
    def __init__(self, name): 
        self.name = name 

    def __str__(self): 
        return self.name 

The Widget class is the core class of the application. The parent ...