Practical Python Design Patterns by Wessel Badenhorst

Author:Wessel Badenhorst
Language: eng
Format: epub
Publisher: Apress, Berkeley, CA

main_function(hd, "1221345439")

Already it is clear that we have a much cleaner solution at hand. We did not have to make any changes to the way each class is connected to the next, and apart from passing on the request, we did not require any changes to be made to the individual execute functions or the main function in order to accommodate the way each class executes the request. We have clearly separated each function into its own unit of code that can be plugged into, or removed from, the chain of classes dealing with the request.

Each handler cares only about its own execution and ignores what happens when another handler executes because of the query. The handler decides in the moment if it should do anything as a result of the request it receives, which leads to increased flexibility in determining which handlers should execute as a result of a query. The best part of this implementation is that handlers can be added and removed at runtime, and when the order is unimportant in terms of the execution queue, you could even shuffle the order of the handlers. This only goes to show, once again, that loosely coupled code is more flexible than tightly coupled code.

To further illustrate this flexibility, we extend the previous program so each class will only do something if it sees that the digit associated with the class name is in the request string.

class CatchAll(object):

def __init__(self):

self.next_to_execute = None

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