`IPv6Interface.ip` loses scope ID information

[relativityspace-jsmith]

Bug report

Bug description:

Hi, I ran into an issue in my code (in multiplemonomials/multicast_expert) because putting an IPv6 address into an IPv6Interface, then accessing it via the ip property loses the scope ID information.

Here's a minimal example:

>> addr = ipaddress.IPv6Address("fe80::%10")
>> addr
IPv6Address('fe80::%10')
>> addr_with_prefix = ipaddress.IPv6Interface((addr, 64))
>> addr_with_prefix
IPv6Interface('fe80::%10/64')
>> addr_with_prefix.ip
IPv6Address('fe80::')

I would expect the last line to return IPv6Address('fe80::%10'), matching the value of addr. Not 100.0% sure this is a bug, but it's certainly something I would not expect since it's not in the documentation. So I'd appreciate if a note about this could be added to the docs if nothing else! Thank you!

Note that this issue is similar, but not the same thing: #88178

CPython versions tested on:

3.11

Operating systems tested on:

Windows

Linked PRs

• gh-129538: Fix IPv6Interface.ip losing scope ID information #129548

[donBarbos]

based on the tests this is expected behavior, so could be closed as not planned
(it could be documented, but it doesn't seem like the tests will be allowed to be changed)

cc @picnixz wdyt?

[picnixz]

I don't think it's a bug. We indeed test the following:

self.assertEqual(str(self.ipv6_scoped_interface.ip),
                 '2001:658:22a:cafe:200::1')

where

ipv6_scoped_interface = ipaddress.IPv6Interface('2001:658:22a:cafe:200:0:0:1%scope/64')

The ip attribute is documented as lacking the network information. In particular, the scope (zone) is also omitted. However, we could possibly add an attribute for extracting the scope as it could be useful. (At least, in my understanding, this should be considered as part of this "extra" information).

Alternatively, we can also document this.

[relativityspace-jsmith]

I think that documenting this behavior and adding a way to extract the scope (and also the address with scope, as passed to the constructor) would work!

[picnixz]

Mmh. Actually, I think the tests I showed are not entirely accurate. We say:

To interoperate with networking interfaces such as the socket module, addresses must be converted to strings or integers. This is handled using the str() and int() builtin functions.

But looking at __str__ for IPv6Address, the scope ID is included:

    def __str__(self):
        ipv4_mapped = self.ipv4_mapped
        if ipv4_mapped is None:
            ip_str = super().__str__()
        else:
            ip_str = self._ipv4_mapped_ipv6_to_str()
        return ip_str + '%' + self._scope_id if self._scope_id else ip_str

In other words, we expect the scope ID to be shown. By the way we can already recover the scope ID from an IPv6 address (which is a baseclass of IPv6Interface). Therefore, .ip should have indeed returned the IPv6 with its scope. So, what I concluded yesterday is actually wrong.

Since IPv6Interface.ip is meant to return an IPv6Address without network information, I actually think it's meant to return everything until the /.