Default output directory.

def _default_output_dir():
  """Default output directory."""
  try:
    dataset_name = gin.query_parameter("inputs.dataset_name")
  except ValueError:
    dataset_name = "random"
  dir_name = "{model_name}_{dataset_name}_{timestamp}".format(
      model_name=gin.query_parameter("train.model").configurable.name,
      dataset_name=dataset_name,
      timestamp=datetime.datetime.now().strftime("%Y%m%d_%H%M"),
  )
  dir_path = os.path.join("~", "trax", dir_name)
  print()
  trax.log("No --output_dir specified")
  return dir_path