Observer Pattern
Intent: Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
Described in ObserverPattern.
Common incarnations of the Observer Pattern use events to notify observers about changes in the subject. A python solution that encapsulates event triggering and subscription and mimics C#-style events can be found [http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/410686 here].