code: def push_slack(self, tokens):
          
          logger.debug("Pushing slack data: %s" % tokens)
  
          bus = self.case.buses[tokens["bus_no"] - 1]
  
          g = Generator(bus)
          g.q_max = tokens["q_max"]
          g.q_min = tokens["q_min"]
          # Optional parameter
  #        if tokens.has_key("status"):
  #        g.online = tokens["status"]
  
          self.case.generators.append(g)
  
          bus.type = "ref"
docs: Finds the slack bus, adds a Generator with the appropriate data
          and sets the bus type to slack.