Learning Python, 3rd Edition

Chapter 10. Introducing Python Statements

Now that you’re familiar with Python’s core built-in object types, this chapter begins our exploration of its fundamental statement forms. As in the previous part, we’ll begin here with a general introduction to statement syntax, and follow up with more details about specific statements in the next few chapters.

In simple terms, statements are the things you write to tell Python what your programs should do. If programs “do things with stuff,” statements are the way you specify what sort of things a program does. Python is a procedural, statement-based language; by combining statements, you specify a procedure that Python performs to satisfy a program’s goals.

Python Program Structure Revisited

Another way to understand the role of statements is to revisit the concept hierarchy introduced in Chapter 4, which talked about built-in objects and the expressions used to manipulate them. This chapter climbs the hierarchy to the next level:

1. Programs are composed of modules.

2. Modules contain statements.

3. Statements contain expressions.

4. Expressions create and process objects.

At its core, Python syntax is composed of statements and expressions. Expressions process objects and are embedded in statements. Statements code the larger logic of a program’s operation—they use and direct expressions to process the objects we studied in the preceding chapters. Moreover, statements are where objects spring into existence (e.g., in expressions within assignment statements), ...