This chapter covered the Adapter design pattern. We use the Adapter pattern for making two (or more) incompatible interfaces compatible. As a motivation, an e-commerce system that should support multiple currencies was mentioned. We use adapters every day for interconnecting devices, charging them, and so on.

Adapter makes things work after they have been implemented. The Grok Python framework and the Traits package use the Adapter pattern for achieving API conformance and interface compatibility, respectively. The open/close principle is strongly connected with these aspects.

In the implementation section, we saw how to achieve interface conformance using the Adapter pattern without modifying the source code of the incompatible model. This is achieved through a generic Adapter class that does the work for us. Although we could use sub-classing (inheritance) to implement the Adapter pattern in the traditional way in Python, this technique is a great alternative.

In the next chapter...