Machine translation model based on RNN (#954)

* RNN no attention model

* Attention model added

* Change as review comments

fluid/neural_machine_translation/rnn_search/args.py

+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserve.
+#
+# 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 absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import argparse
+import distutils.util
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--embedding_dim",
+        type=int,
+        default=512,
+        help="The dimension of embedding table. (default: %(default)d)")
+    parser.add_argument(
+        "--encoder_size",
+        type=int,
+        default=512,
+        help="The size of encoder bi-rnn unit. (default: %(default)d)")
+    parser.add_argument(
+        "--decoder_size",
+        type=int,
+        default=512,
+        help="The size of decoder rnn unit. (default: %(default)d)")
+    parser.add_argument(
+        "--batch_size",
+        type=int,
+        default=32,
+        help="The sequence number of a mini-batch data. (default: %(default)d)")
+    parser.add_argument(
+        "--dict_size",
+        type=int,
+        default=30000,
+        help="The dictionary capacity. Dictionaries of source sequence and "
+        "target dictionary have same capacity. (default: %(default)d)")
+    parser.add_argument(
+        "--pass_num",
+        type=int,
+        default=5,
+        help="The pass number to train. (default: %(default)d)")
+    parser.add_argument(
+        "--learning_rate",
+        type=float,
+        default=0.01,
+        help="Learning rate used to train the model. (default: %(default)f)")
+    parser.add_argument(
+        "--no_attention",
+        action='store_true',
+        help="If set, run no attention model instead of attention model.")
+    parser.add_argument(
+        "--beam_size",
+        type=int,
+        default=3,
+        help="The width for beam searching. (default: %(default)d)")
+    parser.add_argument(
+        "--use_gpu",
+        type=distutils.util.strtobool,
+        default=True,
+        help="Whether to use gpu. (default: %(default)d)")
+    parser.add_argument(
+        "--max_length",
+        type=int,
+        default=50,
+        help="The maximum length of sequence when doing generation. "
+        "(default: %(default)d)")
+    parser.add_argument(
+        "--save_dir",
+        type=str,
+        default="model",
+        help="Specify the path to save trained models.")
+    parser.add_argument(
+        "--save_interval",
+        type=int,
+        default=1,
+        help="Save the trained model every n passes."
+        "(default: %(default)d)")
+    args = parser.parse_args()
+    return args

fluid/neural_machine_translation/rnn_search/attention_model.py

+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserve.
+#
+# 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 absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import paddle.fluid as fluid
+from paddle.fluid.contrib.decoder.beam_search_decoder import *
+
+
+def lstm_step(x_t, hidden_t_prev, cell_t_prev, size):
+    def linear(inputs):
+        return fluid.layers.fc(input=inputs, size=size, bias_attr=True)
+
+    forget_gate = fluid.layers.sigmoid(x=linear([hidden_t_prev, x_t]))
+    input_gate = fluid.layers.sigmoid(x=linear([hidden_t_prev, x_t]))
+    output_gate = fluid.layers.sigmoid(x=linear([hidden_t_prev, x_t]))
+    cell_tilde = fluid.layers.tanh(x=linear([hidden_t_prev, x_t]))
+
+    cell_t = fluid.layers.sums(input=[
+        fluid.layers.elementwise_mul(
+            x=forget_gate, y=cell_t_prev), fluid.layers.elementwise_mul(
+                x=input_gate, y=cell_tilde)
+    ])
+
+    hidden_t = fluid.layers.elementwise_mul(
+        x=output_gate, y=fluid.layers.tanh(x=cell_t))
+
+    return hidden_t, cell_t
+
+
+def seq_to_seq_net(embedding_dim, encoder_size, decoder_size, source_dict_dim,
+                   target_dict_dim, is_generating, beam_size, max_length):
+    """Construct a seq2seq network."""
+
+    def bi_lstm_encoder(input_seq, gate_size):
+        # A bi-directional lstm encoder implementation.
+        # Linear transformation part for input gate, output gate, forget gate
+        # and cell activation vectors need be done outside of dynamic_lstm.
+        # So the output size is 4 times of gate_size.
+        input_forward_proj = fluid.layers.fc(input=input_seq,
+                                             size=gate_size * 4,
+                                             act='tanh',
+                                             bias_attr=False)
+        forward, _ = fluid.layers.dynamic_lstm(
+            input=input_forward_proj, size=gate_size * 4, use_peepholes=False)
+        input_reversed_proj = fluid.layers.fc(input=input_seq,
+                                              size=gate_size * 4,
+                                              act='tanh',
+                                              bias_attr=False)
+        reversed, _ = fluid.layers.dynamic_lstm(
+            input=input_reversed_proj,
+            size=gate_size * 4,
+            is_reverse=True,
+            use_peepholes=False)
+        return forward, reversed
+
+    # The encoding process. Encodes the input words into tensors.
+    src_word_idx = fluid.layers.data(
+        name='source_sequence', shape=[1], dtype='int64', lod_level=1)
+
+    src_embedding = fluid.layers.embedding(
+        input=src_word_idx,
+        size=[source_dict_dim, embedding_dim],
+        dtype='float32')
+
+    src_forward, src_reversed = bi_lstm_encoder(
+        input_seq=src_embedding, gate_size=encoder_size)
+
+    encoded_vector = fluid.layers.concat(
+        input=[src_forward, src_reversed], axis=1)
+
+    encoded_proj = fluid.layers.fc(input=encoded_vector,
+                                   size=decoder_size,
+                                   bias_attr=False)
+
+    backward_first = fluid.layers.sequence_pool(
+        input=src_reversed, pool_type='first')
+
+    decoder_boot = fluid.layers.fc(input=backward_first,
+                                   size=decoder_size,
+                                   bias_attr=False,
+                                   act='tanh')
+
+    cell_init = fluid.layers.fill_constant_batch_size_like(
+        input=decoder_boot,
+        value=0.0,
+        shape=[-1, decoder_size],
+        dtype='float32')
+    cell_init.stop_gradient = False
+
+    # Create a RNN state cell by providing the input and hidden states, and
+    # specifies the hidden state as output.
+    h = InitState(init=decoder_boot, need_reorder=True)
+    c = InitState(init=cell_init)
+
+    state_cell = StateCell(
+        inputs={'x': None,
+                'encoder_vec': None,
+                'encoder_proj': None},
+        states={'h': h,
+                'c': c},
+        out_state='h')
+
+    def simple_attention(encoder_vec, encoder_proj, decoder_state):
+        # The implementation of simple attention model
+        decoder_state_proj = fluid.layers.fc(input=decoder_state,
+                                             size=decoder_size,
+                                             bias_attr=False)
+        decoder_state_expand = fluid.layers.sequence_expand(
+            x=decoder_state_proj, y=encoder_proj)
+        # concated lod should inherit from encoder_proj
+        concated = fluid.layers.concat(
+            input=[encoder_proj, decoder_state_expand], axis=1)
+        attention_weights = fluid.layers.fc(input=concated,
+                                            size=1,
+                                            bias_attr=False)
+        attention_weights = fluid.layers.sequence_softmax(
+            input=attention_weights)
+        weigths_reshape = fluid.layers.reshape(x=attention_weights, shape=[-1])
+        scaled = fluid.layers.elementwise_mul(
+            x=encoder_vec, y=weigths_reshape, axis=0)
+        context = fluid.layers.sequence_pool(input=scaled, pool_type='sum')
+        return context
+
+    @state_cell.state_updater
+    def state_updater(state_cell):
+        # Define the updater of RNN state cell
+        current_word = state_cell.get_input('x')
+        encoder_vec = state_cell.get_input('encoder_vec')
+        encoder_proj = state_cell.get_input('encoder_proj')
+        prev_h = state_cell.get_state('h')
+        prev_c = state_cell.get_state('c')
+        context = simple_attention(encoder_vec, encoder_proj, prev_h)
+        decoder_inputs = fluid.layers.concat(
+            input=[context, current_word], axis=1)
+        h, c = lstm_step(decoder_inputs, prev_h, prev_c, decoder_size)
+        state_cell.set_state('h', h)
+        state_cell.set_state('c', c)
+
+    # Define the decoding process
+    if not is_generating:
+        # Training process
+        trg_word_idx = fluid.layers.data(
+            name='target_sequence', shape=[1], dtype='int64', lod_level=1)
+
+        trg_embedding = fluid.layers.embedding(
+            input=trg_word_idx,
+            size=[target_dict_dim, embedding_dim],
+            dtype='float32')
+
+        # A decoder for training
+        decoder = TrainingDecoder(state_cell)
+
+        with decoder.block():
+            current_word = decoder.step_input(trg_embedding)
+            encoder_vec = decoder.static_input(encoded_vector)
+            encoder_proj = decoder.static_input(encoded_proj)
+            decoder.state_cell.compute_state(inputs={
+                'x': current_word,
+                'encoder_vec': encoder_vec,
+                'encoder_proj': encoder_proj
+            })
+            h = decoder.state_cell.get_state('h')
+            decoder.state_cell.update_states()
+            out = fluid.layers.fc(input=h,
+                                  size=target_dict_dim,
+                                  bias_attr=True,
+                                  act='softmax')
+            decoder.output(out)
+
+        label = fluid.layers.data(
+            name='label_sequence', shape=[1], dtype='int64', lod_level=1)
+        cost = fluid.layers.cross_entropy(input=decoder(), label=label)
+        avg_cost = fluid.layers.mean(x=cost)
+        feeding_list = ["source_sequence", "target_sequence", "label_sequence"]
+        return avg_cost, feeding_list
+
+    else:
+        # Inference
+        init_ids = fluid.layers.data(
+            name="init_ids", shape=[1], dtype="int64", lod_level=2)
+        init_scores = fluid.layers.data(
+            name="init_scores", shape=[1], dtype="float32", lod_level=2)
+
+        # A beam search decoder
+        decoder = BeamSearchDecoder(
+            state_cell=state_cell,
+            init_ids=init_ids,
+            init_scores=init_scores,
+            target_dict_dim=target_dict_dim,
+            word_dim=embedding_dim,
+            input_var_dict={
+                'encoder_vec': encoded_vector,
+                'encoder_proj': encoded_proj
+            },
+            topk_size=50,
+            sparse_emb=True,
+            max_len=max_length,
+            beam_size=beam_size,
+            end_id=1,
+            name=None)
+
+        decoder.decode()
+
+        translation_ids, translation_scores = decoder()
+        feeding_list = ["source_sequence"]
+
+        return translation_ids, translation_scores, feeding_list

fluid/neural_machine_translation/rnn_search/infer.py

+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserve.
+#
+# 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 absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import numpy as np
+import os
+
+import paddle
+import paddle.fluid as fluid
+import paddle.fluid.core as core
+import paddle.fluid.framework as framework
+from paddle.fluid.executor import Executor
+from paddle.fluid.contrib.decoder.beam_search_decoder import *
+
+from args import *
+import attention_model
+import no_attention_model
+
+
+def infer():
+    args = parse_args()
+
+    # Inference
+    if args.no_attention:
+        translation_ids, translation_scores, feed_order = \
+            no_attention_model.seq_to_seq_net(
+            args.embedding_dim,
+            args.encoder_size,
+            args.decoder_size,
+            args.dict_size,
+            args.dict_size,
+            True,
+            beam_size=args.beam_size,
+            max_length=args.max_length)
+    else:
+        translation_ids, translation_scores, feed_order = \
+            attention_model.seq_to_seq_net(
+            args.embedding_dim,
+            args.encoder_size,
+            args.decoder_size,
+            args.dict_size,
+            args.dict_size,
+            True,
+            beam_size=args.beam_size,
+            max_length=args.max_length)
+
+    test_batch_generator = paddle.batch(
+        paddle.reader.shuffle(
+            paddle.dataset.wmt14.test(args.dict_size), buf_size=1000),
+        batch_size=args.batch_size,
+        drop_last=False)
+
+    place = core.CUDAPlace(0) if args.use_gpu else core.CPUPlace()
+    exe = Executor(place)
+    exe.run(framework.default_startup_program())
+
+    model_path = os.path.join(args.save_dir, str(args.pass_num))
+    fluid.io.load_persistables(
+        executor=exe,
+        dirname=model_path,
+        main_program=framework.default_main_program())
+
+    src_dict, trg_dict = paddle.dataset.wmt14.get_dict(args.dict_size)
+
+    feed_list = [
+        framework.default_main_program().global_block().var(var_name)
+        for var_name in feed_order[0:1]
+    ]
+    feeder = fluid.DataFeeder(feed_list, place)
+
+    for batch_id, data in enumerate(test_batch_generator()):
+        # The value of batch_size may vary in the last batch
+        batch_size = len(data)
+
+        # Setup initial ids and scores lod tensor
+        init_ids_data = np.array([0 for _ in range(batch_size)], dtype='int64')
+        init_scores_data = np.array(
+            [1. for _ in range(batch_size)], dtype='float32')
+        init_ids_data = init_ids_data.reshape((batch_size, 1))
+        init_scores_data = init_scores_data.reshape((batch_size, 1))
+        init_recursive_seq_lens = [1] * batch_size
+        init_recursive_seq_lens = [
+            init_recursive_seq_lens, init_recursive_seq_lens
+        ]
+        init_ids = fluid.create_lod_tensor(init_ids_data,
+                                           init_recursive_seq_lens, place)
+        init_scores = fluid.create_lod_tensor(init_scores_data,
+                                              init_recursive_seq_lens, place)
+
+        # Feed dict for inference
+        feed_dict = feeder.feed(map(lambda x: [x[0]], data))
+        feed_dict['init_ids'] = init_ids
+        feed_dict['init_scores'] = init_scores
+
+        fetch_outs = exe.run(framework.default_main_program(),
+                             feed=feed_dict,
+                             fetch_list=[translation_ids, translation_scores],
+                             return_numpy=False)
+
+        # Split the output words by lod levels
+        lod_level_1 = fetch_outs[0].lod()[1]
+        token_array = np.array(fetch_outs[0])
+        result = []
+        for i in xrange(len(lod_level_1) - 1):
+            sentence_list = [
+                trg_dict[token]
+                for token in token_array[lod_level_1[i]:lod_level_1[i + 1]]
+            ]
+            sentence = " ".join(sentence_list[1:-1])
+            result.append(sentence)
+        lod_level_0 = fetch_outs[0].lod()[0]
+        paragraphs = [
+            result[lod_level_0[i]:lod_level_0[i + 1]]
+            for i in xrange(len(lod_level_0) - 1)
+        ]
+
+        for paragraph in paragraphs:
+            print(paragraph)
+
+
+if __name__ == '__main__':
+    infer()

fluid/neural_machine_translation/rnn_search/no_attention_model.py

+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserve.
+#
+# 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 absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import paddle.fluid.layers as layers
+from paddle.fluid.contrib.decoder.beam_search_decoder import *
+
+
+def seq_to_seq_net(embedding_dim, encoder_size, decoder_size, source_dict_dim,
+                   target_dict_dim, is_generating, beam_size, max_length):
+    def encoder():
+        # Encoder implementation of RNN translation
+        src_word = layers.data(
+            name="src_word", shape=[1], dtype='int64', lod_level=1)
+        src_embedding = layers.embedding(
+            input=src_word,
+            size=[source_dict_dim, embedding_dim],
+            dtype='float32',
+            is_sparse=True)
+
+        fc1 = layers.fc(input=src_embedding, size=encoder_size * 4, act='tanh')
+        lstm_hidden0, lstm_0 = layers.dynamic_lstm(
+            input=fc1, size=encoder_size * 4)
+        encoder_out = layers.sequence_last_step(input=lstm_hidden0)
+        return encoder_out
+
+    def decoder_state_cell(context):
+        # Decoder state cell, specifies the hidden state variable and its updater
+        h = InitState(init=context, need_reorder=True)
+        state_cell = StateCell(
+            inputs={'x': None}, states={'h': h}, out_state='h')
+
+        @state_cell.state_updater
+        def updater(state_cell):
+            current_word = state_cell.get_input('x')
+            prev_h = state_cell.get_state('h')
+            # make sure lod of h heritted from prev_h
+            h = layers.fc(input=[prev_h, current_word],
+                          size=decoder_size,
+                          act='tanh')
+            state_cell.set_state('h', h)
+
+        return state_cell
+
+    def decoder_train(state_cell):
+        # Decoder for training implementation of RNN translation
+        trg_word = layers.data(
+            name="target_word", shape=[1], dtype='int64', lod_level=1)
+        trg_embedding = layers.embedding(
+            input=trg_word,
+            size=[target_dict_dim, embedding_dim],
+            dtype='float32',
+            is_sparse=True)
+
+        # A training decoder
+        decoder = TrainingDecoder(state_cell)
+
+        # Define the computation in each RNN step done by decoder
+        with decoder.block():
+            current_word = decoder.step_input(trg_embedding)
+            decoder.state_cell.compute_state(inputs={'x': current_word})
+            current_score = layers.fc(input=decoder.state_cell.get_state('h'),
+                                      size=target_dict_dim,
+                                      act='softmax')
+            decoder.state_cell.update_states()
+            decoder.output(current_score)
+
+        return decoder()
+
+    def decoder_infer(state_cell):
+        # Decoder for inference implementation
+        init_ids = layers.data(
+            name="init_ids", shape=[1], dtype="int64", lod_level=2)
+        init_scores = layers.data(
+            name="init_scores", shape=[1], dtype="float32", lod_level=2)
+
+        # A beam search decoder for inference
+        decoder = BeamSearchDecoder(
+            state_cell=state_cell,
+            init_ids=init_ids,
+            init_scores=init_scores,
+            target_dict_dim=target_dict_dim,
+            word_dim=embedding_dim,
+            input_var_dict={},
+            topk_size=50,
+            sparse_emb=True,
+            max_len=max_length,
+            beam_size=beam_size,
+            end_id=1,
+            name=None)
+        decoder.decode()
+        translation_ids, translation_scores = decoder()
+
+        return translation_ids, translation_scores
+
+    context = encoder()
+    state_cell = decoder_state_cell(context)
+
+    if not is_generating:
+        label = layers.data(
+            name="target_next_word", shape=[1], dtype='int64', lod_level=1)
+
+        rnn_out = decoder_train(state_cell)
+
+        cost = layers.cross_entropy(input=rnn_out, label=label)
+        avg_cost = layers.mean(x=cost)
+
+        feeding_list = ['src_word', 'target_word', 'target_next_word']
+        return avg_cost, feeding_list
+    else:
+        translation_ids, translation_scores = decoder_infer(state_cell)
+        feeding_list = ['src_word']
+        return translation_ids, translation_scores, feeding_list

fluid/neural_machine_translation/rnn_search/train.py

+#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserve.
+#
+# 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 absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import numpy as np
+import time
+import os
+
+import paddle
+import paddle.fluid as fluid
+import paddle.fluid.core as core
+import paddle.fluid.framework as framework
+from paddle.fluid.executor import Executor
+from paddle.fluid.contrib.decoder.beam_search_decoder import *
+
+from args import *
+import attention_model
+import no_attention_model
+
+
+def train():
+    args = parse_args()
+
+    # Training process
+    if args.no_attention:
+        avg_cost, feed_order = no_attention_model.seq_to_seq_net(
+            args.embedding_dim,
+            args.encoder_size,
+            args.decoder_size,
+            args.dict_size,
+            args.dict_size,
+            False,
+            beam_size=args.beam_size,
+            max_length=args.max_length)
+    else:
+        avg_cost, feed_order = attention_model.seq_to_seq_net(
+            args.embedding_dim,
+            args.encoder_size,
+            args.decoder_size,
+            args.dict_size,
+            args.dict_size,
+            False,
+            beam_size=args.beam_size,
+            max_length=args.max_length)
+
+    # clone from default main program and use it as the validation program
+    main_program = fluid.default_main_program()
+    inference_program = fluid.default_main_program().clone()
+
+    optimizer = fluid.optimizer.Adam(
+        learning_rate=args.learning_rate,
+        regularization=fluid.regularizer.L2DecayRegularizer(
+            regularization_coeff=1e-5))
+
+    optimizer.minimize(avg_cost)
+
+    train_batch_generator = paddle.batch(
+        paddle.reader.shuffle(
+            paddle.dataset.wmt14.train(args.dict_size), buf_size=1000),
+        batch_size=args.batch_size,
+        drop_last=False)
+
+    test_batch_generator = paddle.batch(
+        paddle.reader.shuffle(
+            paddle.dataset.wmt14.test(args.dict_size), buf_size=1000),
+        batch_size=args.batch_size,
+        drop_last=False)
+
+    place = core.CUDAPlace(0) if args.use_gpu else core.CPUPlace()
+    exe = Executor(place)
+    exe.run(framework.default_startup_program())
+
+    feed_list = [
+        main_program.global_block().var(var_name) for var_name in feed_order
+    ]
+    feeder = fluid.DataFeeder(feed_list, place)
+
+    def validation():
+        # Use test set as validation each pass
+        total_loss = 0.0
+        count = 0
+        val_feed_list = [
+            inference_program.global_block().var(var_name)
+            for var_name in feed_order
+        ]
+        val_feeder = fluid.DataFeeder(val_feed_list, place)
+
+        for batch_id, data in enumerate(test_batch_generator()):
+            val_fetch_outs = exe.run(inference_program,
+                                     feed=val_feeder.feed(data),
+                                     fetch_list=[avg_cost],
+                                     return_numpy=False)
+
+            total_loss += np.array(val_fetch_outs[0])[0]
+            count += 1
+
+        return total_loss / count
+
+    for pass_id in range(1, args.pass_num + 1):
+        pass_start_time = time.time()
+        words_seen = 0
+        for batch_id, data in enumerate(train_batch_generator()):
+            words_seen += len(data) * 2
+
+            fetch_outs = exe.run(framework.default_main_program(),
+                                 feed=feeder.feed(data),
+                                 fetch_list=[avg_cost])
+
+            avg_cost_train = np.array(fetch_outs[0])
+            print('pass_id=%d, batch_id=%d, train_loss: %f' %
+                  (pass_id, batch_id, avg_cost_train))
+
+        pass_end_time = time.time()
+        test_loss = validation()
+        time_consumed = pass_end_time - pass_start_time
+        words_per_sec = words_seen / time_consumed
+        print("pass_id=%d, test_loss: %f, words/s: %f, sec/pass: %f" %
+              (pass_id, test_loss, words_per_sec, time_consumed))
+
+        if pass_id % args.save_interval == 0:
+            model_path = os.path.join(args.save_dir, str(pass_id))
+            if not os.path.isdir(model_path):
+                os.makedirs(model_path)
+
+            fluid.io.save_persistables(
+                executor=exe,
+                dirname=model_path,
+                main_program=framework.default_main_program())
+
+
+if __name__ == '__main__':
+    train()