Python Cookbook

Chapter 4. Files

Introduction

Credit: Mark Lutz, author of Programming Python, co-author of Learning Python

Behold the file—one of the first things that any reasonably pragmatic programmer reaches for in a programming language’s toolbox. Because processing external files is a very real, tangible task, the quality of file-processing interfaces is a good way to assess the practicality of a programming tool.

As the examples in this chapter attest, Python shines here too. In fact, files in Python are supported in a variety of layers: from the built-in open function’s standard file object, to specialized tools in standard library modules such as os, to third-party utilities available on the Web. All told, Python’s arsenal of file tools provides several powerful ways to access files in your scripts.

File Basics

In Python, a file object is an instance of a built-in type. The built-in function open creates and returns a file object. The first argument, a string, specifies the file’s path (i.e., the filename preceded by an optional directory path). The second argument to open, also a string, specifies the mode in which to open the file. For example:

input = open('data', 'r')
output = open('/tmp/spam', 'w')

open accepts a file path in which directories and files are separated by slash characters (/), regardless of the proclivities of the underlying operating system. On systems that don’t use slashes, you can use a backslash character (\) instead, but there’s no real reason to do so. Backslashes ...