docs: def fetch_followers(account_file, outfile, limit, do_loop):
      """ Fetch up to limit followers for each Twitter account in
      account_file. Write results to outfile file in format:
  
      screen_name user_id follower_id_1 follower_id_2 ..."""
      print('Fetching followers for accounts in %s' % account_file)
      niters = 1
      while True:
          outf = gzip.open(outfile, 'wt')
          for screen_name in iter_lines(account_file):
              timestamp = datetime.datetime.now().isoformat()
              print('collecting followers for', screen_name)
              followers = twutil.collect.followers_for_screen_name(screen_name, limit)
              if len(followers) > 0:
                  outf.write('%s %s %s\n' % (timestamp, screen_name, ' '.join(followers)))
                  outf.flush()
              else:
                  print('unknown user', screen_name)
          outf.close()
          if not do_loop:
              return
          else:
              if niters == 1:
                  outfile = '%s.%d' % (outfile, niters)
              else:
                  outfile = outfile[:outfile.rindex('.')] + '.%d' % niters
              niters += 1