docs: def bin_to_mac(bin, size=6):
      """Convert 6 bytes into a MAC string.
  
      Args:
          bin (str): hex string of lenth 6.
  
      Returns:
          str: String representation of the MAC address in lower case.
  
      Raises:
          Exception: if ``len(bin)`` is not 6.
      """
      if len(bin) != size:
          raise Exception("Invalid MAC address: %s" % (bin))
      return ':'.join([binascii.hexlify(o) for o in bin])