import tensorflow as tf


    if bidirectional:
        lstm_cell_bw = tf.contrib.rnn.LSTMBlockFusedCell(num_units=num_units, **kwargs)
        lstm_cell_bw = tf.contrib.rnn.TimeReversedFusedRNN(lstm_cell_bw)
        outputs_bw, (hidden_bw, output_bw) = lstm_cell_bw(t, dtype=tf.float32, sequence_length=nwords)
        outputs = tf.concat([outputs_fw, outputs_bw], axis=-1)
