docs: def _update_port_group_info(self, switches=None):
          """Refresh data on switch interfaces' port group membership"""
          if switches is None:
              switches = self._switches.keys()
          for switch_ip in switches:
              client = self._switches.get(switch_ip)
              ret = self._run_eos_cmds(['show interfaces'], client)
              if not ret or len(ret) == 0:
                  LOG.warning("Unable to retrieve interface info for %s",
                              switch_ip)
                  continue
              intf_info = ret[0]
              self._port_group_info[switch_ip] = intf_info.get('interfaces', {})