SpiffSignal is a Python module that implements a simple signal/event mechanism:
from SpiffSignal import Trackable
class WatchMe(Trackable):
def do_something(self):
self.signal_emit('did-something', 'hello world')
def my_callback(arg):
print arg
foo = WatchMe()
foo.signal_connect('did-something', my_callback)
foo.do_something()