pypubsub

PyPubSub provides a publish - subscribe API that facilitates the development of
event-based (also known as message-based) applications. PyPubSub supports sending and
receiving messages between objects of an application, as well as a variety of
advanced features that facilitate debugging and maintaining topics and messages
in larger applications.

See the PyPubSub website (http://pubsub.sourceforge.net/) for
further details. Downoad from the Files link or from the Python Cheeseshop.