See the chapters titled "Internet Protocols and Support" and "Internet Data Handling" in the Library Reference Manual. Python has many modules that will help you build server-side and client-side web systems.
A summary of available frameworks is maintained by Paul Boddie at http://www.python.org/cgi-bin/moinmoin/WebProgramming .
Cameron Laird maintains a useful set of pages about Python web technologies at http://phaseit.net/claird/comp.lang.python/web_python.
The Web Programming topic guide also points to many useful resources.
CATEGORY: library