µTidylib and mxTidy – Python interfaces to html tidy library to clean up HTML documents.

html5lib A HTML5-compliant library for parsing arbitarily-broken HTML to a range of tree formats including minidom, elementtree (including lxml) and BeautifulSoup

BeautifulSoup – a permissive HTML parser.

Don’t use HTMLParser (Python 2.x) or html.parser (Python 3.x) on HTML that might be invalid! That way lies pain. Either clean it up (using tidy), or use a different parser.

urllib, urllib2, and httplib in the standard library.

ClientCookie, ClientForm, and Mechanize are higher-level libraries for writing a web client.

mechanoid a mechanize fork.

libxml2dom can parse HTML by employing libxml2’s liberal HTML parser.

Grab a document from the web - from the Python Cookbook

Python web-client programming general FAQs.

urllib – Open arbitrary resources by URL

urllib2 – extensible library for opening URLs