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, may be simpler, and thus more suitable when you don't need any of the benefits of object-oriented programming. With Python, you can mix and match the two paradigms.

Python today is in transition between two slightly different object models. This chapter mainly describes the new-style, or new object model, which is simpler, more regular, more powerful, and the one I recommend you always use; whenever I speak of classes or instances, without explicitly specifying otherwise, I mean new-style classes or instances. However, for backward compatibility, the default object model in all Python 2.x versions, for every value of x, is the legacy object model, also known as the classic or old-style object model; the new-style object model will become the default (and the legacy one will disappear) in a few years, when Python 3.0 comes out. Therefore, in each section, after describing how the new-style object model works, this chapter covers the small differences between the new and legacy object models, and discusses how to use both object models with Python 2.x. Finally, the chapter covers special methods, in "Special Methods" on page 104, and then two advanced concepts known as decorators, in "Decorators" on page 115, and metaclasses, in "Metaclasses" on page 116.