Learning Python, 3rd Edition

Chapter 2. How Python Runs Programs

This chapter and the next give a quick look at program execution—how you launch code, and how Python runs it. In this chapter, we’ll study the Python interpreter. Chapter 3 will then show you how to get your own programs up and running.

Startup details are inherently platform-specific, and some of the material in this chapter may not apply to the platform you work on, so you should feel free to skip parts not relevant to your intended use. Likewise, more advanced 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 this chapter away as “for future reference.” For the rest of you, let’s learn how to run some code.

Introducing the Python Interpreter

So far, I’ve mostly been talking about Python as a programming language. But, as currently implemented, it’s also a software package 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 software logic between your code and the computer hardware on your machine.

When the Python package is installed on your machine, it generates a number of components—minimally, an interpreter and a support library. Depending on how you use it, the Python interpreter may take the form of an executable program, or a set of libraries linked into another program. ...