import tensorflow as tf

  def _build_sampler(self, prev_c=None, prev_h=None, use_bias=False):
    """Build the sampler ops and the log_prob ops."""

    print ("-" * 80)
    print ("Build controller sampler")

    anchors = tf.TensorArray(
      tf.float32, size=self.num_cells + 2, clear_after_read=False)
    anchors_w_1 = tf.TensorArray(
      tf.float32, size=self.num_cells + 2, clear_after_read=False)
    arc_seq = tf.TensorArray(tf.int32, size=self.num_cells * 4)
    if prev_c is None:
      assert prev_h is None, "prev_c and prev_h must both be None"
      prev_c = [tf.zeros([1, self.lstm_size], tf.float32)
                for _ in range(self.lstm_num_layers)]
      prev_h = [tf.zeros([1, self.lstm_size], tf.float32)
                for _ in range(self.lstm_num_layers)]
    inputs = self.g_emb

    for layer_id in range(2):
      next_c, next_h = stack_lstm(inputs, prev_c, prev_h, self.w_lstm)
      prev_c, prev_h = next_c, next_h
      anchors = anchors.write(layer_id, tf.zeros_like(next_h[-1]))
      anchors_w_1 = anchors_w_1.write(
        layer_id, tf.matmul(next_h[-1], self.w_attn_1))

