Create hparams.

def create_hparams():
  """Create hparams."""
  if FLAGS.use_tpu and "tpu" not in FLAGS.hparams_set:
    tf.logging.warn("Not all hyperparameter sets work on TPU. "
                    "Prefer hparams_sets with a '_tpu' suffix, "
                    "e.g. transformer_tpu, if available for your model.")
  hparams_path = os.path.join(FLAGS.output_dir, "hparams.json")
  return trainer_lib.create_hparams(FLAGS.hparams_set, FLAGS.hparams,
                                    hparams_path=hparams_path)