code: def _ip_int_from_prefix(self, prefixlen=None):
          
          if prefixlen is None:
              prefixlen = self._prefixlen
          return self._ALL_ONES ^ (self._ALL_ONES >> prefixlen)
docs: Turn the prefix length netmask into a int for comparison.
  
          Args:
              prefixlen: An integer, the prefix length.
  
          Returns:
              An integer.