Parsing 4th level domain from file which contain domain

dnslv4.py

"""
host.txt generated from command: host -l domain (unix like)
"""
try:
    f = open("host.txt", "r")    
    try:
        lines = f.readlines()
        before = ""
        count = 0
        for line in lines:
            domain = line[0:line.find(' ')]
            if (domain != before):
                if (domain.count('.') == 3):
                    count += 1
                    print "{} : {}".format(domain, count)
            before = domain
    finally:
        print count
        f.close()
except IOError:
    pass