Find available 3ch reddit usernames (fixed)

#!/usr/bin/env python

import httplib
import string

def exists(username):
  c = httplib.HTTPConnection("www.reddit.com")
  c.request("HEAD", "/user/" + username)
  r = c.getresponse().status
  assert r in [200, 404], "WTF just happened?"
  return r == 200

cc = string.ascii_lowercase + string.digits + "-_"
all_3ch = set(x + y + z for x in cc for y in cc for z in cc)

for user in all_3ch:
  if not exists(user):
    print user