Fix the bug of BidirectionalCell

CONTRIBUTORS.md

@@ -192,6 +192,7 @@ List of Contributors
 * [Rahul Padmanabhan](https://github.com/rahul3)
 * [Yuxi Hu](https://github.com/yuxihu)
 * [Harsh Patel](https://github.com/harshp8l)
+* [Xiao Wang](https://github.com/BeyonderXX)
 
 Label Bot
 ---------

tests/python/unittest/test_gluon_rnn.py

@@ -243,6 +243,34 @@ def test_bidirectional():
     assert outs == [(10, 200), (10, 200), (10, 200)]
 
 
+def test_bidirectional_unroll_valid_length():
+    # Test BidirectionalCell.
+    # In 1.3.1 version, after hybridize( ), BidirectionalCell would failed when pass valid_length to unroll( ).
+    class BiLSTM(gluon.nn.HybridBlock):
+        def __init__(self, rnn_size, time_step, **kwargs):
+            super(BiLSTM, self).__init__(**kwargs)
+            self.time_step = time_step
+            with self.name_scope():
+                self.bi_lstm = gluon.rnn.BidirectionalCell(
+                    gluon.rnn.LSTMCell(rnn_size, prefix='rnn_l0_'),
+                    gluon.rnn.LSTMCell(rnn_size, prefix='rnn_r0_'),
+                    output_prefix='lstm_bi_')
+
+        def hybrid_forward(self, F, inputs, valid_len):
+            outputs, states = self.bi_lstm.unroll(self.time_step, inputs, valid_length=valid_len,
+                                                  layout='TNC', merge_outputs='True')
+            return outputs, states
+
+    rnn_size, time_step = 100, 3
+    net = BiLSTM(rnn_size, time_step)
+    net.initialize()
+    net.hybridize()
+    inputs_data = mx.nd.random.uniform(shape=(3, 10, 50))
+    valid_len = mx.nd.array(range(1, 11))
+    outputs, _ = net(inputs_data, valid_len)
+    assert outputs.shape == (3, 10, 200)
+
+
 @assert_raises_cudnn_not_satisfied(min_version='5.1.10')
 def test_layer_bidirectional():
     class RefBiLSTM(gluon.Block):