问tf.contrib.seq2seq.gather_tree是如何工作的？

EN

def gather_tree_py(values, parents):
  """Gathers path through a tree backwards from the leave nodes. Used
  to reconstruct beams given their parents."""

  beam_length = values.shape[0]
  num_beams = values.shape[1]
  res = np.zeros_like(values)
  res[-1, :] = values[-1, :]
  for beam_id in range(num_beams):
    parent = parents[-1][beam_id]
    for level in reversed(range(beam_length - 1)):
      res[level, beam_id] = values[level][parent]
      parent = parents[level][parent]
  return np.array(res).astype(values.dtype)


def gather_tree(values, parents):
  """Tensor version of gather_tree_py"""

  res = tf.py_func(
      func=gather_tree_py, inp=[values, parents], Tout=values.dtype)
  res.set_shape(values.get_shape().as_list())
  return res