code: def update(self, *args, **kw):
          
          super(Interface, self).update(*args, **kw)
          self._engine._del_cache()
          return self
docs: Update/save this interface information back to SMC. When interface
          changes are made, especially to sub interfaces, call `update` on
          the top level interface.
  
          Example of changing the IP address of an interface::
  
              >>> engine = Engine('sg_vm')
              >>> interface = engine.physical_interface.get(1)
              >>> interface.zone_ref = zone_helper('mynewzone')
              >>> interface.update()
  
          :raises UpdateElementFailed: failure to save changes
          :return: Interface