Learning Python, 6th Edition

Chapter 2. How Python Runs Programs

This chapter and the next cover program execution—how you launch code and how Python runs it. In this chapter, we’ll begin by studying how the Python interpreter executes programs in general, from an abstract vantage point. With that perspective in hand, Chapter 3 will dive into the nuts and bolts of getting your own programs up and running.

Startup details are inherently platform specific, and some of the material in these two chapters may not apply to the ways you’ll be using Python, so you should feel free to skip parts not relevant to your goals. Likewise, readers who have used similar tools in the past and prefer to get to the meat of the language quickly may want to file some of these chapters away for future reference. For the rest of us, let’s take a brief look at the way that Python will run our code, before we get into the details of writing or running it.

Introducing the Python Interpreter

So far, we’ve mostly been talking about Python as a programming language. In its most widely used form, though, it’s also a software system called an interpreter. An interpreter is a kind of program that executes other programs. When you write a Python program, the Python interpreter reads your program and carries out the instructions it contains. In effect, the interpreter is a layer of logic between your code and the computer hardware on your machine.

When Python is installed, it generates a number of components—minimally, an interpreter and ...