These two calls are currently Unix-only in the socket module. However, Windows supports them starting with Vista:
https://docs.microsoft.com/en-us/windows/desktop/api/netioapi/nf-netioapi-if_indextoname
https://docs.microsoft.com/en-us/windows/desktop/api/netioapi/nf-netioapi-if_nametoindex

I checked with ctypes and they do seem to work. Unfortunately, if_nameindex is not implemented.

I've created a PR for this issue. Few changes are needed to implement these functions on Windows.

Is it worth also implementing if_nameindex() using (I assume) GetIfTable2Ex [1]? Or maybe just the simpler GetIfTable is sufficient - I'm not sure exactly what semantics Unix if_nameindex() has, whether it includes all logical adapters.

[1]: https://docs.microsoft.com/en-us/windows/desktop/api/netioapi/nf-netioapi-getiftable2ex

That would be fantastic, but I did not dare asking for it :)

This is how the output of if_nameindex looks on my Fedora 29:

[(1, 'lo'), (2, 'enp0s31f6'), (3, 'wlp4s0'), (4, 'virbr0'), (5, 'virbr0-nic'), (12, 'tun0')]

It includes the loopback, two real adapters (ethernet and wifi) and devices apparently created by libvirt.

This is how it looks on my OpenStack testing environment:

[(1, 'lo'), (2, 'eth0'), (3, 'virbr0'), (4, 'virbr0-nic'), (5, 'ovs-system'), (6, 'br-int'), (7, 'br-ex'), (8, 'brbm'), (9, 'br-tun'), (14, 'ovs-node-0i1'), (15, 'tap-node-0i1'), (16, 'ovs-node-0i2'), (17, 'tap-node-0i2'), (18, 'ovs-node-1i1'), (19, 'tap-node-1i1'), (20, 'ovs-node-1i2'), (21, 'tap-node-1i2'), (22, 'ovs-node-2i1'), (23, 'tap-node-2i1'), (24, 'ovs-node-2i2'), (25, 'tap-node-2i2'), (26, 'ovs-tap'), (27, 'brbm-tap'), (34, 'br-inspector'), (35, 'brbm-inspector'), (55, 'macvtap2'), (56, 'macvtap3'), (79, 'macvtap0'), (80, 'macvtap1')]

It seems to actually include everything.

Well, it turns out that implementing if_nameindex() on Windows using GetIfTable2Ex() was also quite simple. I've updated the PR.

Great, thanks Zackery! (And thanks for the ping - I don't notice GitHub notifications.)

Had a few comments about error handling, but it looks great.

Thanks, Steve. I've addressed your comments on the PR.

New changeset 8f96c9f8ed2a4795e34b333411451e24f28f74d2 by Steve Dower (Zackery Spytz) in branch 'master':
bpo-37007: Implement socket.if_nametoindex(), if_indextoname() and if_nameindex() on Windows (GH-13522)
https://github.com/python/cpython/commit/8f96c9f8ed2a4795e34b333411451e24f28f74d2