code: def start(self, flow):
          
          state = State.objects.create(flow=flow, 
              current_node=flow.state_graph.root)
          flow.state_graph.root.data.rule.on_enter(state)
          return state
docs: Factory method for a running state based on a flow.  Creates and
          returns a ``State`` object and calls the associated
          :func:`Rule.on_enter` method.
  
          :param flow: 
              :class:`Flow` which defines this state machine
          :returns: 
              newly created instance