Write the Understand Sentiment book example with stacked LSTM using new API (#10355)

* Add understand apiu with stacked lstm for new API

* Complete exam

python/paddle/fluid/tests/book/understand_sentiment/notest_understand_sentiment_stacked_lstm.py

+# Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+
+import paddle
+import paddle.fluid as fluid
+from functools import partial
+
+CLASS_DIM = 2
+EMB_DIM = 128
+HID_DIM = 512
+STACKED_NUM = 3
+
+
+def stacked_lstm_net(data, input_dim, class_dim, emb_dim, hid_dim, stacked_num):
+    assert stacked_num % 2 == 1
+
+    emb = fluid.layers.embedding(
+        input=data, size=[input_dim, emb_dim], is_sparse=True)
+
+    fc1 = fluid.layers.fc(input=emb, size=hid_dim)
+    lstm1, cell1 = fluid.layers.dynamic_lstm(input=fc1, size=hid_dim)
+
+    inputs = [fc1, lstm1]
+
+    for i in range(2, stacked_num + 1):
+        fc = fluid.layers.fc(input=inputs, size=hid_dim)
+        lstm, cell = fluid.layers.dynamic_lstm(
+            input=fc, size=hid_dim, is_reverse=(i % 2) == 0)
+        inputs = [fc, lstm]
+
+    fc_last = fluid.layers.sequence_pool(input=inputs[0], pool_type='max')
+    lstm_last = fluid.layers.sequence_pool(input=inputs[1], pool_type='max')
+
+    prediction = fluid.layers.fc(input=[fc_last, lstm_last],
+                                 size=class_dim,
+                                 act='softmax')
+    return prediction
+
+
+def inference_network(word_dict):
+    data = fluid.layers.data(
+        name="words", shape=[1], dtype="int64", lod_level=1)
+
+    dict_dim = len(word_dict)
+    net = stacked_lstm_net(data, dict_dim, CLASS_DIM, EMB_DIM, HID_DIM,
+                           STACKED_NUM)
+    return net
+
+
+def train_network(word_dict):
+    prediction = inference_network(word_dict)
+    label = fluid.layers.data(name="label", shape=[1], dtype="int64")
+    cost = fluid.layers.cross_entropy(input=prediction, label=label)
+    avg_cost = fluid.layers.mean(cost)
+    accuracy = fluid.layers.accuracy(input=prediction, label=label)
+    return avg_cost, accuracy
+
+
+def train(use_cuda, save_path):
+    BATCH_SIZE = 128
+    EPOCH_NUM = 5
+
+    word_dict = paddle.dataset.imdb.word_dict()
+
+    train_data = paddle.batch(
+        paddle.reader.shuffle(
+            paddle.dataset.imdb.train(word_dict), buf_size=1000),
+        batch_size=BATCH_SIZE)
+
+    test_data = paddle.batch(
+        paddle.dataset.imdb.test(word_dict), batch_size=BATCH_SIZE)
+
+    def event_handler(event):
+        if isinstance(event, fluid.EndIteration):
+            if (event.batch_id % 10) == 0:
+                avg_cost, accuracy = trainer.test(reader=test_data)
+
+                print('BatchID {1:04}, Loss {2:2.2}, Acc {3:2.2}'.format(
+                    event.batch_id + 1, avg_cost, accuracy))
+
+                if accuracy > 0.01:  # Low threshold for speeding up CI
+                    trainer.params.save(save_path)
+                    return
+
+    place = fluid.CUDAPlace(0) if use_cuda else fluid.CPUPlace()
+    trainer = fluid.Trainer(
+        partial(train_network, word_dict),
+        optimizer=fluid.optimizer.Adagrad(learning_rate=0.002),
+        place=place,
+        event_handler=event_handler)
+
+    trainer.train(train_data, EPOCH_NUM, event_handler=event_handler)
+
+
+def infer(use_cuda, save_path):
+    params = fluid.Params(save_path)
+    place = fluid.CUDAPlace(0) if use_cuda else fluid.CPUPlace()
+    word_dict = paddle.dataset.imdb.word_dict()
+    inferencer = fluid.Inferencer(
+        partial(inference_network, word_dict), params, place=place)
+
+    def create_random_lodtensor(lod, place, low, high):
+        data = np.random.random_integers(low, high,
+                                         [lod[-1], 1]).astype("int64")
+        res = fluid.LoDTensor()
+        res.set(data, place)
+        res.set_lod([lod])
+        return res
+
+    lod = [0, 4, 10]
+    tensor_words = create_random_lodtensor(
+        lod, place, low=0, high=len(word_dict) - 1)
+    results = inferencer.infer({'words': tensor_words})
+    print("infer results: ", results)
+
+
+def main(use_cuda):
+    if use_cuda and not fluid.core.is_compiled_with_cuda():
+        return
+    save_path = "understand_sentiment_stacked_lstm.inference.model"
+    train(use_cuda, save_path)
+    infer(use_cuda, save_path)
+
+
+if __name__ == '__main__':
+    for use_cuda in (False, True):
+        main(use_cuda=use_cuda)