Chapter 5. Object-Oriented Python

Python is an object-oriented programming language. Unlike some other object-oriented languages, Python doesn't force you to use the object-oriented paradigm exclusively. Python also supports procedural programming with modules and functions, so you can select the most suitable programming paradigm for each part of your program. Generally, the object-oriented paradigm is suitable when you want to group state (data) and behavior (code) together in handy packets of functionality. It's also useful when you want to use some of Python's object-oriented mechanisms covered in this chapter, such as inheritance or special methods. The procedural paradigm, based on modules and functions, tends to be simpler and is more suitable when you don't need any of the benefits of object-oriented programming. With Python, you often mix and match the two paradigms.

Python 2.2 and 2.3 are in transition between two slightly different object models. This chapter starts by describing the classic object model, which was the only one available in Python 2.1 and earlier and is still the default model in Python 2.2 and 2.3. The chapter then covers the small differences that define the powerful new-style object model and discusses how to use the new-style object model with Python 2.2 and 2.3. Because the new-style object model builds on the classic one, you'll need to understand the classic model before you can learn about the new model. Finally, the chapter covers special methods for both the classic and new-style object models, as well as metaclasses for Python 2.2 and later.

The new-style object model will become the default in a future version of Python. Even though the classic object model is still the default, I suggest you use the new-style object model when programming with Python 2.2 and later. Its advantages over the classic object model, while small, are measurable, and there are practically no compensating disadvantages. Therefore, it's simpler just to stick to the new-style object model, rather than try to decide which model to use each time you code a new class.