Pygame is a set of Python modules designed for writing games. Pygame adds functionality on top of the excellent SDL library. This allows you to create fully featured games and multimedia programs in the python language. Pygame is highly portable and runs on nearly every platform and operating system.
Pygame is free. Released under the LGPL licence, you can create open source, free, freeware, shareware, and commercial games with it. Over 1000 open source games have been released that use pygame, so there are lots of examples to learn from.