def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
def _restore_vars(v_list, t_list):
  """Restore variables in v_list from t_list."""
  ops = []
  for v, t in zip(v_list, t_list):
    ops.append(v.assign(t))
  return ops