docs: def bind (self, event, callback):
          """
          Bind an event to a call function and ensure that it is called for the
          specified event
          :param event: the event that should trigger the callback
          :type event: str
          :param callback: the function that should be called
          :rtype callback: function
          """
          if self._events.has_key(event):
              self._events[event].append(callback)
          else:
              self._events[event] = [callback]