code: def _discover_mac(self):
          
          mac = None
          mac_reversed = None
          cmd = MAGIC + DISCOVERY
          resp = self._udp_transact(cmd, self._discovery_resp,
                                    broadcast=True,
                                    timeout=DISCOVERY_TIMEOUT)
          if resp:
              (mac, mac_reversed) = resp
          if mac is None:
              raise S20Exception("Couldn't discover {}".format(self.host))
          return (mac, mac_reversed)
docs: Discovers MAC address of device.
  
          Discovery is done by sending a UDP broadcast.
          All configured devices reply. The response contains
          the MAC address in both needed formats.
  
          Discovery of multiple switches must be done synchronously.
  
          :returns: Tuple of MAC address and reversed MAC address.