tldify.py

import sys, urllib.request

url = "https://data.iana.org/TLD/tlds-alpha-by-domain.txt"
local_filename, headers = urllib.request.urlretrieve(url)
tlds = open(local_filename).readlines()
tlds = [tld.strip() for tld in tlds]

if len(sys.argv) > 1:
    domain = sys.argv[1]
else:
    domain = input("Enter a domain name: ")

substitunion_count = 0
for tld in tlds:
    tld = tld.lower()
    if domain.lower().endswith(tld):
        substitunion_count += 1
        print(domain[:domain.index(tld)] + "." + tld)

if substitunion_count == 0:
    print("No top level domain name substitutions were found")