class_docstr: Error: reader not found
code: def __str__(self):
      msg = "Reader {} Not Found.\nAvailiable readers:\n".format(
          self.reader_name
      )
      for reader in self.avail_readers:
          msg += "  {}\n".format(reader)
      return msg
  
file_path: PaddleHub/modules/video/classification/videotag_tsn_lstm/resource/reader/reader_utils.py
label_desc: Use image node_id 2 for calling the ReaderNotFoundError obj's underlying member method code with example usage: obj.__str__() and returns: msg