Python_Standard_Library.pdf

Preface

"We'd like to pretend that "Fredrik" is a role, but even hundreds of

volunteers couldn't possibly keep up. No, "Fredrik" is the result of

crossing an http server with a spam filter with an emacs whatsit and

some other stuff besides"

Gordon McMillan, June 1998

The Python 2.0 distribution comes with an extensive standard library, comprising over 200 modules.

This book provides a brief description of each module, plus one or more sample scripts showing how to

use it. All in all, this book contains 360 sample scripts.

About this Book

"Those people who have nothing better to do than post on the Internet

all day long are rarely the ones who have the most insights"

Jacob Nielsen, December 1998

Since I first stumbled upon Python some five years ago, I've spent hundreds of hours answering

questions on the comp.lang.python newsgroup. Maybe someone found a module that might be

exactly what he wanted, but he couldn't really figure out how to use it. Maybe someone had picked the

wrong module for the task. Or maybe someone tried to reinvent the wheel. Often, a short sample script

could be much more helpful than a pointer to the reference documentation.

After posting a couple of scripts each week, for a number of years, you end up with a rather large

collection of potentially useful scripts. What you'll find in this book are the best parts from over 3,000

newsgroup messages. You'll also find hundreds of new scripts added to make sure every little nook and

cranny of the standard library has been fully covered.

I've worked hard to make the scripts easy to understand and adaptable. I've intentionally kept the

annotations as short as possible. If you want more background, there's plenty of reference material

shipped with most Python distributions. In this book, the emphasis is on the code.

Comments, suggestions, and bug reports are welcome. Send them to fredrik@pythonware.com . I read

all mail as soon as it arrives, but it might take a while until I get around to answer.

For updates, addenda, and other information related to this book, point your favorite web browser to

http://www.pythonware.com/people/fredrik/librarybook.htm

Python Standard Library

What about Tkinter?

This book covers the entire standard library, except the (optional) Tkinter user interface library. There

are several reasons for this, mostly related to time, space, and the fact that I'm working on several

other Tkinter documentation projects.

For current status on these projects, see http://www.pythonware.com/people/fredrik/tkinterbook.htm

Production details

This book was written in DocBook SGML. I used a variety of tools, including Secret Labs'

PythonWorks, and Excosoft Documentor, James Clark's Jade DSSSL processor, and Norm Walsh's

DocBook stylesheets. And a bunch of Python scripts, of course.

Thanks to my referees: Tim Peters, Guido van Rossum, David Ascher, Mark Lutz, and Rael Dornfest,

and the PythonWare crew: Matthew Ellis, Håkan Karlsson, and Rune Uhlin.

Thanks to Lenny Muellner, who turned my SGML files into the book you see before you, and to

Christien Shanreaw, who pulled all the different text and code files together for the book and the CD-

ROM.

About the Examples

Unless otherwise noted, all examples run under Python 1.5.2 and Python 2.0. I've tried not to depend

on internal details, and I expect most scripts to work with upcoming 2.x versions as well.

The examples have been tested on Windows, Solaris, and Linux. Except for a few scripts that depend

on platform specific modules, the examples should work right out of the box on most other platforms

as well. (If you find something that doesn't work as expected, let me know!)

All code is copyrighted. Of course, you're free to use one or more modules in your own programs, just

don't forget where you got them.

Most script files are named after the module they're using, followed by the string " -example- " and a

unique "serial number". Note that the scripts sometimes appear out of order; it's done this way on

purpose, to match the filenames used in an earlier version of this book, (the eff-bot guide to) The

Standard Python Library .

You'll find copies of all scripts on the CD provided with this book. For updates and more information,

see http://www.pythonware.com/people/fredrik/librarybook.htm.

Python Standard Library: Core Modules

1-1

Core Modules

"Since the functions in the C runtime library are not part of the Win32

API, we believe the number of applications that will be affected by this

bug to be very limited"

Microsoft, January 1999

Overview

Python's standard library covers a wide range of modules. Everything from modules that are as much a

part of the Python language as the types and statements defined by the language specification, to

obscure modules that are probably useful only to a small number of programs.

This section describes a number of fundamental standard library modules. Any larger Python program

is likely to use most of these modules, either directly or indirectly.

Built-in Functions and Exceptions

Two modules are even more basic than all other modules combined: the __builtin__ module defines

built-in functions (like len , int , and range ), and the exceptions module defines all built-in

exceptions.

Python imports both modules when it starts up, and makes their content available for all programs.

Operating System Interface Modules

There are a number of modules providing platform-independent interfaces to the underlying operating

system. They are modeled after the POSIX standard API and the standard C library.

The modules in this group include os , which provides file and process operations, os.path which

offers a platform-independent way to pull apart and put together file names, and time which provides

functions to work with dates and times.

To some extent, networking and thread support modules could also belong in this group, but they are

not supported by all Python implementations.

Python Standard Library

Python Standard Library: Core Modules

1-2

Type Support Modules

Several built-in types have support modules in the standard library. The string module implements

commonly used string operations, the math module provides math operations and constants, and the

cmath module does the same for complex numbers.

Regular Expressions

The re module provides regular expressions support for Python. Regular expressions are string

patterns written in a special syntax, which can be used to match strings, and extract substrings.

Language Support Modules

sys gives you access to various interpreter variables, such as the module search path, and the

interpreter version. operator provides functional equivalents to many built-in operators. copy allows

you to copy objects. And finally, gc gives you more control over the garbage collector facilities in

Python 2.0.

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