unshorten links in file with Python

unshorten.py

#!/usr/bin/env python

# This is for Py2k.  For Py3k, use http.client and urllib.parse instead, and
# use // instead of / for the division
import sys
import httplib
import urlparse
import re

def unshorten_url(url):
    if hasattr(url, 'group'):
        url = url.group(0)
    parsed = urlparse.urlparse(url)
    h = httplib.HTTPConnection(parsed.netloc)
    resource = parsed.path
    if parsed.query != "":
        resource += "?" + parsed.query
    h.request('HEAD', resource )
    response = h.getresponse()
    if response.status/100 == 3 and response.getheader('Location'):
        return unshorten_url(response.getheader('Location')) # changed to process chains of short urls
    else:
        return url

def unshorten_file(file_in, file_out):

    with open(file_in) as f_in, open(file_out, 'w') as f_out:
        for line in f_in:
            f_out.write(re.sub(r'http://([^\n ,]+)', unshorten_url, line))
    return 0

if __name__ == '__main__':
    if len(sys.argv) != 3:
        sys.exit('Usage: %s <input> <output>' % sys.argv[0])

    unshorten_file(sys.argv[1], sys.argv[2])