PyPubSub provides a publish-subscribe API to facilitate event-based or
message-based architecture in a single-process application. It is pure
Python and works on Python 3.3+. It is centered on the notion of a
topic; senders publish messages of a given topic, and listeners
subscribe to messages of a given topic, all inside the same process.
The package also supports a variety of advanced features that
facilitate debugging and maintaining topics and messages in larger
desktop-based or server-based applications.