Python in a Nutshell

Chapter 4. The Python Language

This chapter is a quick guide to the Python language. To learn Python from scratch, I suggest you start with Learning Python, by Mark Lutz and David Ascher (O’Reilly). If you already know other programming languages and just want to learn the specifics of Python, this chapter is for you. I’m not trying to teach Python here, so we’re going to cover a lot of ground at a pretty fast pace.

Lexical Structure

The lexical structure of a programming language is the set of basic rules that govern how you write programs in that language. It is the lowest-level syntax of the language and specifies such things as what variable names look like and what characters are used for comments. Each Python source file, like any other text file, is a sequence of characters. You can also usefully see it as a sequence of lines, tokens, or statements. These different syntactic views complement and reinforce each other. Python is very particular about program layout, especially with regard to lines and indentation, so you’ll want to pay attention to this information if you are coming to Python from another language.

Lines and Indentation

A Python program is composed of a sequence of logical lines, each made up of one or more physical lines. Each physical line may end with a comment. A pound sign (#) that is not inside a string literal begins a comment. All characters after the # and up to the physical line end are part of the comment, and the Python interpreter ignores them. A ...