0
 ?÷     pass in a bytes (str in Python 2) instead of'
                ' a unicode object?'
            )
            raise AddressValueError(msg % (address, address_len,
                                           expected_len, self._version))

    @classmethod
    def _ip_int_from_prefix(cls, prefixlen):
        """Turn the prefix length into a bitwise netmask

        Args:
            prefixlen: An integer, the prefix length.

        Returns:
            An integer.

        """
        return cls._ALL_ONES ^ (cls._ALL_ONES >> prefixlen)

    @classmethod
    def _prefix_from_ip_int(cls, ip_int):
        """Return prefix length from the bitwise netmask.

        Args:
            ip_int: An integer, the netmask in expanded bitwise format

        Returns:
            An integer, the prefix length.

        Raises:
            ValueError: If the input intermingles zeroes & ones
        """
        trailing_zeroes = _count_righthand_zero_bits(ip_int,
                                                     cls._max_prefixlen)
        prefixlen = cls._max_prefixlen - trailing_zeroes
        leading_ones = ip_int >> trailing_zeroes
        all_ones = (1 << prefixlen) - 1
        if leading_ones != all_ones:
            byteslen = cls._max_prefixlen // 8
            details = _compat_to_bytes(ip_int, byteslen, 'big')
            msg = 'Netmask pattern %r mixes zeroes & ones'
            raise ValueError(msg % details)
        return prefixlen

    @classmethod
    def _report_invalid_netmask(cls, netmask_str):
        msg = '%r is not a valid netmask' % netmask_str
        raise NetmaskValueError(msg)

    @classmethod
    def _prefix_from_prefix_string(cls, prefixlen_str):
        """Return prefix length from a numeric string

        Args:
            prefixlen_str: The string to be converted

        Returns:
            An integer, the prefix length.

        Raises:
            NetmaskValueError: If the input is not a valid netmask
        """
        # int allows a leading +/- as well as surrounding whitespace,
        # so we ensure that isn't the case
        if not _BaseV4._DECIMAL_DIGITS.issuperset(prefixlen_str):
            cls._report_invalid_netmask(prefixlen_str)
        try:
            prefixlen = int(prefixlen_str)
        except ValueError:
            cls._report_invalid_netmask(prefixlen_str)
        if not (0 <= prefixlen <= cls._max_prefixlen):
            cls._report_invalid_netmask(prefixlen_str)
        return prefixlen

    @classmethod
    def _prefix_from_ip_string(cls, ip_str):
        """Turn a netmask/hostmask string into a prefix length

        Args:
            ip_str: The netmask/hostmask to be converted

        Returns:
            An integer, the prefix length.

        Raises:
            NetmaskValueError: If the input is not a valid netmask/hostmask
        """
        # Parse the netmask/hostmask like an IP address.
        try:
            ip_int = cls._ip_int_from_string(ip_str)
        except AddressValueError:
            cls._report_invalid_netmask(ip_str)

        # Try matching a netmask (this would be /1*0*/ as a bitwise regexp).
        # Note that the two ambiguous cases (all-ones and all-zeroes) are
        # treated as netmasks.
        try:
            return cls._prefix_from_ip_int(ip_int)
        except ValueError:
            pass

        # Invert the bits, and try matching a /0+1+/ hostmask instead.
        ip_int ^= cls._ALL_ONES
        try:
            return cls._prefix_from_ip_int(ip_int)
        except ValueError:
            cls._report_invalid_netmask(ip_str)

    def __reduce__(self):
        return self.__class__, (_compat_str(self),)


class _BaseAddress(_IPAddressBase):

    """A generic IP object.

    This IP class contains the version independent methods which are
    used by single IP addresses.
    """

    __slots__ = ()

    def __int__(self):
        return self._ip

    def __eq__(self, other):
        try:
            return (self._ip == other._ip and
                    self._version == other._version)
        except AttributeError: