docs: def valid_mac_addr(addr):
      ''' Validates a mac address'''
      if not isinstance(addr, six.string_types):
          return False
      valid = re.compile(r'''
                        (^([0-9A-F]{2}[:]){5}([0-9A-F]{2})$)
                        ''',
                        re.VERBOSE | re.IGNORECASE)
      return valid.match(addr) is not None