code: def iter_follower_file(fname):
      
      with open(fname, 'rt') as f:
          for line in f:
              parts = line.split()
              if len(parts) > 3:
                  yield parts[1].lower(), set(int(x) for x in parts[2:])
docs: Iterator from a file of follower information and return a tuple of screen_name, follower ids.
      File format is:
      <iso timestamp> <screen_name> <follower_id1> <follower_ids2> ...