Make sure that the data is prepared and the vocab is generated.

def prepare_to_generate(self, data_dir, tmp_dir):
    """Make sure that the data is prepared and the vocab is generated."""
    self.get_or_create_vocab(data_dir, tmp_dir)
    self.train_text_filepaths(tmp_dir)
    self.dev_text_filepaths(tmp_dir)