There are some bugs in interface.py:
* All methods raise "NotImplemented" instead of "NotImplementedError()"
* There are two methods called "retreieve" instead of "retrieve"
Since these interfaces are not defined as abstract base classes these bugs are not really relevant but it won't hurt to fix them.
p.s.: Please let me know if I should make patch.
p.s. 2: Branch with fixes at github: http://github.com/bastikr/python-puremvc/tree/master/trunk/