Python extract domain name from URL

Question

hello,

how would you extract the domain name from a URL, excluding any subdomains?

My initial simplistic attempt was:

'.'.join(urlparse.urlparse(url).netloc.split('.')[-2:])

This works for http://www.foo.com, but not http://www.foo.com.au. Is there a way to do this properly without using special knowledge about valid TLDs or country codes (because they change).

thanks

Answer 1

No, there is no "intrinsic" way of knowing that (e.g.) zap.co.it is a subdomain (because Italy's registrar DOES sell domains such as co.it) while zap.co.uk isn't (because the UK's registrar DOESN'T sell domains such as co.uk, but only like zap.co.uk).

You'll just have to use an auxiliary table (or online source) to tell you which TLD's behave peculiarly like UK's and Australia's -- there's no way of divining that from just staring at the string without such extra semantic knowledge (of course it can change eventually, but if you can find a good online source that source will also change accordingly, one hopes!-).

Answer 2

There are many, many TLD's. Here's the list:

http://data.iana.org/TLD/tlds-alpha-by-domain.txt

Here's another list

http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains

Here's another list

http://www.iana.org/domains/root/db/

Answer 3

using this file of effective tlds which someone else found on mozzila's website:

from __future__ import with_statement
from urlparse import urlparse

# load tlds, ignore comments and empty lines:
with open("effective_tld_names.dat.txt") as tldFile:
    tlds = [line.strip() for line in tldFile if line[0] not in "/\n"]

def getDomain(url, tlds):
    urlElements = urlparse(url)[1].split('.')
    # urlElements = ["abcde","co","uk"]

    for i in range(-len(urlElements),0):
        lastIElements = urlElements[i:]
        #    i=-3: ["abcde","co","uk"]
        #    i=-2: ["co","uk"]
        #    i=-1: ["uk"] etc

        candidate = ".".join(lastIElements) # abcde.co.uk, co.uk, uk
        wildcardCandidate = ".".join(["*"]+lastIElements[1:]) # *.co.uk, *.uk, *
        exceptionCandidate = "!"+candidate

        # match tlds: 
        if (exceptionCandidate in tlds):
            return ".".join(urlElements[i:]) 
        if (candidate in tlds or wildcardCandidate in tlds):
            return ".".join(urlElements[i-1:])
            # returns "abcde.co.uk"

    raise ValueError("Domain not in global list of TLDs")

print getDomain("http://abcde.co.uk",tlds)

results in:

abcde.co.uk

I'd appreciate it if someone let me know which bits of the above could be rewritten in a more pythonic way. For example, there must be a better way of iterating over the lastIElements list, but I couldn't think of one. I also don't know if ValueError is the best thing to raise. Comments?