code: def _is_hostmask(self, ip_str):
          
          bits = ip_str.split('.')
          try:
              parts = [x for x in map(int, bits) if x in self._valid_mask_octets]
          except ValueError:
              return False
          if len(parts) != len(bits):
              return False
          if parts[0] < parts[-1]:
              return True
          return False
docs: Test if the IP string is a hostmask (rather than a netmask).
  
          Args:
              ip_str: A string, the potential hostmask.
  
          Returns:
              A boolean, True if the IP string is a hostmask.