Using socket.getaddrinfo to look up IP addresses

As sort of promised in the last entry, here's the Python code to look up IPv4 and IPv6 addresses for a host, using getaddrinfo(). As usual, this is condensed for WanderingThoughts and omits a modicum of error checking.

import socket

def gethostips(host, type=None):
    ips = set()
    if type:
        types = (type,)
    else:
        types = (socket.AF_INET,
                 socket.AF_INET6)
    for t in types:
        try: 
            res = socket.getaddrinfo(host, None,
                           t, socket.SOCK_STREAM)
        except socket.error:
            continue
        nips = set([x[4][0] for x in res])
        ips.update(nips)
    return list(ips)

Passed just the hostname, it returns both IPv4 and IPv6 addresses; passed an optional type argument, it returns just addresses of that type. If there's nothing available, you get an empty list. Addresses are returned in some arbitrary order that mixes IPv4 and IPv6 addresses; I'm going to call this a feature, although in real code I might be tempted to change it so that all IPv4 addresses are returned either first or last.

(Besides, if you care about pretty-printing things you want to have some kind of sorting function that puts IP addresses in ascending order.)

This isn't what you want for making connections; instead, this is the kind of utility function that you need when verifying the hostnames of IP addresses, when some of the IP addresses you're dealing with are now IPv6 addresses because you've started to IPv6-enable your programs. This intended use is one reason why it returns an empty list if getaddrinfo() returns nothing instead of raising an exception.

(Note that a really good IPv6 hostname lookup function is more complicated than the IPv4 version; done properly, it should convert IPv4 compatible and IPv4 mapped addresses into IPv4 addresses and do an IPv4 hostname lookup for them.)