SQLAlchemy or SQLObject - Object oriented access to several different database systems
DatabaseInterfaces - Direct Python interfaces to relational and non-relational database backends
See also DatabaseProgramming for guidance on choosing a database backend system
CTypes - A package for calling the functions of dlls/shared libraries. Now included with Python 2.5 and up.
Cython is an extension language for the CPython runtime. It translates Python code to fast C code and supports calling external C and C++ code natively. As opposed to ctypes, it requires a C compiler to translate the generated code.
PyGame - Principal wrapper of the SDL library.
Python Imaging Library (PIL) - Supports many file formats, and provides powerful image processing and graphics capabilities.
pyqtgraph - Pure-python graphics library for scientific applications with image/video display, multidimensional image slicing, and interactive manipulation tools.
asyncoro - Asynchronous, concurrent programming framework with coroutines with thread-like interface
Gevent - Coroutine-based network library
TwistedMatrix - Event-driven networking framework
RPyC - Transparent RPC/distributed-computing framework
PyRO - powerful OO RPC
HTTPLib2 - A comprehensive HTTP client library that supports many features left out of other HTTP libraries, like httplib on the standard library.
Celery - Distributed task queue for out of band processing/RPC and more.
Psyco - Psyco can speed up the execution of any Python code (x86 only).
PyInstaller - Packages Python programs into stand-alone executables, under Windows, Linux and Irix.
py2app - Creates stand-alone apps (like py2exe for Mac)
PyObjC - Bridge between the Python and Objective-C. Most important usage of this is writing Cocoa GUI applications on Mac OS X in pure Python
PyWin32 - Python extensions for Windows.
Py2exe - Converts python scripts into executable windows programs, able to run without requiring a python installation.
Chaco - Creates interactive plots
gnuplot.py - Based on gnuplot
Matplotlib - Production quality output in a wide variety of formats
Plotly - Interactive, publication-quality, web based charts
PyX - Postscript and PDF output, (La)TeX integration
ReportLab includes a charting package
pyqtgraph - Pure-python plotting and graphics library based on PyQt and numpy.
The SciPy topical software page has a longer list.
http://docutils.sourceforge.net/docs/user/tools.html#rst2s5-py - Create HTML slides from .rst files
http://seld.be/notes/introducing-slippy-html-presentations - For your Python presentations in browser
See RdfLibraries for a list of available RDF processing solutions.
Visual Python - Offers real-time 3D output, is easily usable by novice programmers, excellent for physics.
SciPy - Includes modules for graphics and plotting, optimization, integration, special functions, signal and image processing, genetic algorithms, ODE solvers, and others.
Python Bindings for R - R is a well known, open source (GPL 2) statistical package. RPy has two versions. Version 2 is still in development but is already usable.
PyIMSL is a collection of Python wrappers to the mathematical and statistical algorithms in the IMSL C Numerical Library. Developers can use Python, PyIMSL and the IMSL C Numerical Library for rapid prototyping. PyIMSL Studio is a complete packaged, supported and documented development environment designed for deploying mathematics and statistics prototype models into production applications. PyIMSL Studio includes the PyIMSL wrappers, the IMSL C Numerical Library, a Python distribution and a selection of open source python modules useful for prototype analytical development. PyIMSL Studio is available for download at no charge for non-commercial use or for commercial evaluation.
Python Path - Wraps the functionality of the os.path module and provides something more convenient.
Requests - An improvement upon urllib etc., for sending HTTP requests.
Dateutil - Provides powerful extensions to the datetime module.
sh - Can call any external program as if it were a function.
DocOpt - Command line arguments parser, with declarative approach (docstring).
PyLibrary - Collection of Libraries useful for Python developers.
ThreadPool - Intuitive approach to threads, well-explained.
See the ParallelProcessing page for other multiprocessing or parallel processing approaches.
psutil - cross-platform library for retrieving information on running processes and system utilization (CPU, memory, disks, network) in Python.
Django - High-level web framework.
Pyramid - Turbogears, Pylons, Repoz.bfg merged as Pyramid.
TurboGears - Rapid web development megaframework.
Pylons - A lightweight web framework emphasizing flexibility and rapid development.
web2py - High-level framework for agile development.
Flask - microframework for Python based on Werkzeug, Jinja 2. (It's BSD licensed)
See a more complete list of topics on the WebProgramming page and frameworks on the WebFrameworks page.
ClientForm - "ClientForm is a Python module for handling HTML forms on the client side, useful for parsing HTML forms, filling them in and returning the completed forms to the server. It developed from a port of Gisle Aas' Perl module HTML::Form, from the libwww-perl library, but the interface is not the same." - from the website.
lxml.html has support for dealing with forms in HTML documents
See also the WebProgramming and WebFrameworks pages.
Beautiful Soup - HTML/XML parser designed for quick turnaround projects like screen-scraping, will accept bad markup.
PyQuery - implements jQuery in Python; faster than BeautifulSoup, apparently.
mxTidy - HTML cleanup tool. This is a library version of the popular HTML Tidy command-line application which will convert HTML (even badly formatted) into e.g. XHTML.
lxml.html is a very fast, easy-to-use and versatile library for handling (and fixing up) HTML
See also PythonXml for related tools.
openflow - A workflow engine for Zope 2.
Goflow - A workflow engine for Django, with same design as openflow.
ElementTree - The Element type is a simple but flexible container object, designed to store hierarchical data structures, such as simplified XML infosets, in memory. --Note: Python 2.5 and up has ElementTree in the Standard Library--
lxml is a very fast, easy-to-use and versatile library for XML handling that is mostly compatible with but much more feature-rich than ElementTree