Introducing Python Object Types

This chapter begins our tour of the Python language. In an informal sense, in Python, we do things with stuff. “Things” take the form of operations like addition and concatenation, and “stuff” refers to the objects on which we perform those operations. In this part of the book, our focus is on that stuff, and the things our programs can do with it.

Somewhat more formally, in Python, data takes the form of objects—either built-in objects that Python provides, or objects we create using Python or external language tools such as C extension libraries. Although we’ll firm up this definition later, objects are essentially just pieces of memory, with values and sets of associated operations.

Because objects are the most fundamental notion in Python programming, we’ll start this chapter with a survey of Python’s built-in object types.

By way of introduction, however, 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:

1. Programs are composed of modules.
   
2. Modules contain statements.
   
3. Statements contain expressions. 
   
4. Expressions create and process objects.

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.