code: def check_actors(self):
          
          actors = []
          for actor in self.owner.actors:
              if actor.skip:
                  continue
              actors.append(actor)
          if len(actors) == 0:
              return
          if not self.allow_source and base.is_source(actors[0]):
              raise Exception("Actor '" + actors[0].full_name + "' is a source, but no sources allowed!")
          for i in xrange(1, len(actors)):
              if not isinstance(actors[i], InputConsumer):
                  raise Exception("Actor does not accept any input: " + actors[i].full_name)
docs: Checks the actors of the owner. Raises an exception if invalid.