Before we get to the code, let’s first establish a clear picture of how this chapter fits into the overall Python picture. From a more concrete perspective, Python programs can be decomposed into modules, statements, expressions, and objects, as follows:
The discussion of modules in Chapter 3 introduced the highest level of this hierarchy. This part’s chapters begin at the bottom—exploring both built-in objects and the expressions you can code to use them.
We’ll move on to study statements in the next part of the book, though we will find that they largely exist to manage the objects we’ll meet here. Moreover, by the time we reach classes in the OOP part of this book, we’ll discover that they allow us to define new object types of our own, by both using and emulating the object types we will explore here. Because of all this, built-in objects are a mandatory point of embarkation for all Python journeys.
Traditional introductions to programming often stress its three pillars of sequence (“Do this, then that”), selection (“Do this if that is true”), and repetition (“Do this many times”). Python has tools in all three categories, along with some for definition—of functions and classes. These themes may help you organize your thinking early on, but they are a bit artificial and simplistic. Expressions such as comprehensions, for example, are both repetition and selection; some of these terms have other meanings in Python; and many later concepts won’t seem to fit this mold at all. In Python, the more strongly unifying principle is objects, and what we can do with them. To see why, read on.