code: def change_id(self, new_id_for_id):
          
          if len(set(new_id_for_id.values())) < len(new_id_for_id):
              raise ValueError('each id must be unique.')
  
          for new_id in new_id_for_id.itervalues():
              if self.ping(new_id):
                  raise ValueError('id {} is already used.'.format(new_id))
  
          self._change_id(new_id_for_id)
  
          for motor_id, new_id in new_id_for_id.iteritems():
              if motor_id in self._known_models:
                  self._known_models[new_id] = self._known_models[motor_id]
                  del self._known_models[motor_id]
              if motor_id in self._known_mode:
                  self._known_mode[new_id] = self._known_mode[motor_id]
                  del self._known_mode[motor_id]
docs: Changes the id of the specified motors (each id must be unique on the bus).