Turn an IPv6 ip_str into an integer.

        Args:
            ip_str: A string, the IPv6 ip_str.

        Returns:
            A long, the IPv6 ip_str.

        Raises:
            AddressValueError: if ip_str isn't a valid IPv6 Address.

def _ip_int_from_string(self, ip_str):
        """Turn an IPv6 ip_str into an integer.

        Args:
            ip_str: A string, the IPv6 ip_str.

        Returns:
            A long, the IPv6 ip_str.

        Raises:
            AddressValueError: if ip_str isn't a valid IPv6 Address.

        """
        parts = ip_str.split(':')

        # An IPv6 address needs at least 2 colons (3 parts).
        if len(parts) < 3:
            raise AddressValueError(ip_str)

        # If the address has an IPv4-style suffix, convert it to hexadecimal.
        if '.' in parts[-1]:
            ipv4_int = IPv4Address(parts.pop())._ip
            parts.append('%x' % ((ipv4_int >> 16) & 0xFFFF))
            parts.append('%x' % (ipv4_int & 0xFFFF))

        # An IPv6 address can't have more than 8 colons (9 parts).
        if len(parts) > self._HEXTET_COUNT + 1:
            raise AddressValueError(ip_str)

        # Disregarding the endpoints, find '::' with nothing in between.
        # This indicates that a run of zeroes has been skipped.
        try:
            skip_index, = (
                [i for i in xrange(1, len(parts) - 1) if not parts[i]] or
                [None])
        except ValueError:
            # Can't have more than one '::'
            raise AddressValueError(ip_str)

        # parts_hi is the number of parts to copy from above/before the '::'
        # parts_lo is the number of parts to copy from below/after the '::'
        if skip_index is not None:
            # If we found a '::', then check if it also covers the endpoints.
            parts_hi = skip_index
            parts_lo = len(parts) - skip_index - 1
            if not parts[0]:
                parts_hi -= 1
                if parts_hi:
                    raise AddressValueError(ip_str)  # ^: requires ^::
            if not parts[-1]:
                parts_lo -= 1
                if parts_lo:
                    raise AddressValueError(ip_str)  # :$ requires ::$
            parts_skipped = self._HEXTET_COUNT - (parts_hi + parts_lo)
            if parts_skipped < 1:
                raise AddressValueError(ip_str)
        else:
            # Otherwise, allocate the entire address to parts_hi.  The endpoints
            # could still be empty, but _parse_hextet() will check for that.
            if len(parts) != self._HEXTET_COUNT:
                raise AddressValueError(ip_str)
            parts_hi = len(parts)
            parts_lo = 0
            parts_skipped = 0

        try:
            # Now, parse the hextets into a 128-bit integer.
            ip_int = 0L
            for i in xrange(parts_hi):
                ip_int <<= 16
                ip_int |= self._parse_hextet(parts[i])
            ip_int <<= 16 * parts_skipped
            for i in xrange(-parts_lo, 0):
                ip_int <<= 16
                ip_int |= self._parse_hextet(parts[i])
            return ip_int
        except ValueError:
            raise AddressValueError(ip_str)