Generate source and target data from a single file.

def tabbed_parsing_character_generator(tmp_dir, train):
  """Generate source and target data from a single file."""
  character_vocab = text_encoder.ByteTextEncoder()
  filename = "parsing_{0}.pairs".format("train" if train else "dev")
  pair_filepath = os.path.join(tmp_dir, filename)
  return text_problems.text2text_generate_encoded(
      text_problems.text2text_txt_tab_iterator(pair_filepath), character_vocab)