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Step 4: Customizing Behavior by Subclassing

At this point, our class captures much of the OOP machinery in Python: it makes instances, provides behavior in methods, and even does a bit of operator overloading now to intercept print operations in __str__. It effectively packages our data and logic together into a single, self-contained software component, making it easy to locate code and straightforward to change it in the future. By allowing us to encapsulate behavior, it also allows us to factor that code to avoid redundancy and its associated maintenance headaches.

The only major OOP concept it does not yet capture is customization by inheritance. In some sense, we’re already doing inheritance, because instances inherit methods from their classes. To demonstrate the real power of OOP, though, we need to define a superclass/subclass relationship that allows us to extend our software and replace bits of inherited behavior. That’s the main idea behind OOP, after all; by fostering a coding model based upon customization of work already done, it can dramatically cut development time.