Python in a Nutshell

Chapter 18. Client-Side Network Protocol Modules

A program can work on the Internet as a client (a program that accesses resources) or as a server (a program that makes services available). Both kinds of program deal with protocol issues, such as how to access and communicate data, and with data formatting issues. For order and clarity, the Python library deals with these issues in several different modules. This book will cover the topics in separate chapters. This chapter deals with the modules in the Python library that support protocol issues of client programs.

Nowadays, data access can often be achieved most simply through Uniform Resource Locators (URLs). Python supports URLs with modules urlparse, urllib, and urllib2. For rarer cases, when you need fine-grained control of data access protocols normally accessed via URLs, Python supplies modules httplib and ftplib. Protocols for which URLs are often insufficient include mail (modules poplib and smtplib), Network News (module nntplib), and Telnet (module telnetlib). Python also supports the XML-RPC protocol for distributed computing with module xmlrpclib.

URL Access

A URL identifies a resource on the Internet. A URL is a string composed of several optional parts, called components, known as scheme, location, path, query, and fragment. A URL with all its parts looks something like:

scheme://lo.ca.ti.on/pa/th?query#fragment

For example, in http://www.python.org:80/faq.cgi?src=fie, the scheme is http, the location ...