code: def add_single(self, address, rank=1, nodeid=1, ospf_area=None, **kwargs):
          
          lb = self.create(address, rank, nodeid, ospf_area, **kwargs)
          self._engine.nodes[0].data[self.typeof].append(lb.data)
          self._engine.update()
docs: Add a single loopback interface to this engine. This is used
          for single or virtual FW engines.
          
          :param str address: ip address for loopback
          :param int nodeid: nodeid to apply. Default to 1 for single FW
          :param str, Element ospf_area: ospf area href or element
          :raises UpdateElementFailed: failure to create loopback address
          :return: None