#!/usr/bin/env pythonimport fileinput, refrom collections import defaultdictdef print_urls(allurls, referer, indent=0):  urls = allurls[referer]  for url in urls:    print ' '*indent + referer    if url in allurls:      print_urls(allurls, url, indent+2)def main():  log_re = re.compile(r'<GET (.*?)> /(referer: (.*?)/)')  allurls = defaultdict(list)  for l in fileinput.input():    m = log_re.search(l)    if m:      url, ref = m.groups()      allurls[ref] += [url]  print_urls(allurls, 'None')main()