Chapter 27. A More Realistic Example

We’ll dig into more class syntax details in the next chapter. Before we do, though, I’d like to show you a more realistic example of classes in action that’s more practical than what we’ve seen so far. In this chapter, we’re going to build a set of classes that do something more concrete—recording and processing information about people. As you’ll see, what we call instances and classes in Python programming can often serve the same roles as records and programs in more traditional terms.

Specifically, in this chapter we’re going to code two classes:

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  • Person—a class that creates and processes information about people
  • Manager—a customization of Person that modifies inherited behavior

Along the way, we’ll make instances of both classes and test out their functionality. When we’re done, I’ll show you a nice example use case for classes—we’ll store our instances in a shelve object-oriented database, to make them permanent. That way, you can use this code as a template for fleshing out a full-blown personal database written entirely in Python.

Besides actual utility, though, our aim here is also educational: this chapter provides a tutorial on object-oriented programming in Python. Often, people grasp the last chapter’s class syntax on paper, but have trouble seeing how to get started when confronted with having to code a new class from scratch. Toward this end, we’ll take it one step at a time here, to help you learn the basics; we’ll build up the classes gradually, so you can see how their features come together in complete programs.

In the end, our classes will still be relatively small in terms of code, but they will demonstrate all of the main ideas in Python’s OOP model. Despite its syntax details, Python’s class system really is largely just a matter of searching for an attribute in a tree of objects, along with a special first argument for functions.