Updated list of valid TLDs (Top Level Domains). Python script grabs the IANA database and formats it into a set datatype.

get_valid_tlds.py

# requirements.txt
# pip install requests
# pip install BeautifulSoup4

import codecs
import requests
from bs4 import BeautifulSoup

PER_LINE = 12

text = requests.get('http://www.iana.org/domains/root/db').text
soup = BeautifulSoup(text)
x = soup.find('table', {'id': 'tld-table'})
tlds = [anchor.text for anchor in x.find_all('a')]

with codecs.open('legal_tlds.py', 'w', encoding='utf8') as f:

    f.write(u'# -*- coding: utf-8 -*-\n')
    f.write(u'TLDS = set([\n')

    for i, tld in enumerate(tlds):
        print tld.encode('utf8')

        tld = tld.lstrip('.')

        if i % PER_LINE == 0:
            f.write('    ')

        f.write(u'\'%s\',' % tld)
        if i % PER_LINE == (PER_LINE - 1):
            f.write('\n')
        else:
            f.write(' ')

    f.write(u'])\n')

Please don't use script above. Resulting list will contains test, retired and unassigned TLDs.