code: def get_or_create_vocab(self, data_dir, tmp_dir, force_get=False):
      
      # We assume that vocab file is present in data_dir directory where the
      # data generated will be stored.
      vocab_filepath = os.path.join(data_dir, self.vocab_filename)
      encoder = text_encoder.SubwordTextEncoder(vocab_filepath)
      return encoder
docs: Get vocab for distill problems.