The http.cookies module implements a parser for cookies that is mostly RFC 2109 compliant. The implementation is a little less strict than the standard because MSIE 3.0x does not support the entire standard.
The urllib.request module provides an API for using Internet resources identified by URLs. It is designed to be extended by individual applications to support new protocols or add variations to existing protocols (such as handling HTTP basic authentication).
The io module provides access to the built-in open() function and the classes used to implement file-based input and output operations. The classes are decomposed in such a way that they can be recombined for alternate purposes, for example to enable writing Unicode data to a network socket.
The importlib module includes functions that the underlying implementation of Python’s import mechanism for loading code in packages and modules, all implemented in Python. It is one access point to importing modules dynamically, and useful in some cases where the name of the module that needs to be imported is unknown when the code is written (for example, for plugins or extensions to an application).
http.server uses classes from socketserver to create base classes for making HTTP servers. HTTPServer can be used directly, but the BaseHTTPRequestHandler is intended to be extended to handle each protocol method (GET, POST, etc.).
robotparser implements a parser for the robots.txt file format, including a function that checks if a given user agent can access a resource. It is intended for use in well-behaved spiders, or other crawler applications that need to either be throttled or otherwise restricted.
Python’s unittest module is based on the XUnit framework design by Kent Beck and Erich Gamma. The same pattern is repeated in many other languages, including C, Perl, Java, and Smalltalk. The framework implemented by unittest supports fixtures, test suites, and a test runner to enable automated testing.