def _is_valid_netmask(self, prefixlen):
        try:
            prefixlen = int(prefixlen)
        except ValueError:
            return False
        return 0 <= prefixlen <= self._max_prefixlen
Verify that the netmask/prefixlen is valid.
dataset/ETHPy150Open anandology/pyjamas/pyjs/src/pyjs/lib/ipaddr.py/IPv6Network._is_valid_netmask