'Return netmask as an integer.
>>> print hex(IP(\'195.185.0.0/16\').netmask().int())
0xFFFF0000L'

def netmask(self):

    if (self._ipversion == 4):
        locallen = (32 - self._prefixlen)
    elif (self._ipversion == 6):
        locallen = (128 - self._prefixlen)
    else:
        raise ValueError('only    IPv4    and    IPv6    supported')
    return (((2 ** self._prefixlen) - 1) << locallen)
