def get_encoder_from_vocab(vocab_filepath):
  """Get encoder from vocab file.

  If vocab is not found in output dir, it will be copied there by
  copy_vocab_to_output_dir to clarify the vocab used to generate the data.

  Args:
    vocab_filepath: path to vocab, either local or cns

  Returns:
    A SubwordTextEncoder vocabulary object. None if the output_parallel_text
    is set.
  """
  if not tf.gfile.Exists(vocab_filepath):
    raise ValueError("Vocab file does not exist: {}.".format(vocab_filepath))

  tf.logging.info("Found vocab file: %s", vocab_filepath)
  encoder = text_encoder.SubwordTextEncoder(vocab_filepath)
  return encoder
Get encoder from vocab file.

  If vocab is not found in output dir, it will be copied there by
  copy_vocab_to_output_dir to clarify the vocab used to generate the data.

  Args:
    vocab_filepath: path to vocab, either local or cns

  Returns:
    A SubwordTextEncoder vocabulary object. None if the output_parallel_text
    is set.
  
tensor2tensor/data_generators/wiki_revision_utils.py