This chapter covered the Decorator pattern and its relation to the Python programming language. We use the Decorator pattern as a convenient way of extending the behavior of an object without using inheritance. Python extends the Decorator concept even more, by allowing us to extend the behavior of any callable (function, method, or class) without using inheritance or composition. We can use the built-in decorator feature of Python.

We have seen a few examples of objects that are decorated in reality, like guns and cameras. From a software point of view, both Django and Grok use decorators for achieving different goals, such as controlling HTTP compression and caching.

The Decorator pattern is a great solution for implementing cross-cutting concerns, because they are generic and do not fit well into the OOP paradigm. We mentioned many categories of cross-cutting concerns in the Use cases section. In fact, in the Implementation section a cross-cutting concern was demonstrated: memoization...