<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_token_encoder(vocab_dir, vocab_name, filename):
 """Reads from file and returns a `TokenTextEncoder` for the vocabulary."""

  vocab_path = os.path.join(vocab_dir, vocab_name)
  if not tf.gfile.Exists(vocab_path):
    _build_vocab(filename, vocab_path, 10000)
  return text_encoder.TokenTextEncoder(vocab_path)