def load_model(model, ckpt, session, name):
start_time = time.time()
model.saver.restore(session, ckpt)
session.run(tf.tables_initializer())
utils.print_out(" loaded %s model parameters from %s, time %.2fs" %
(name, ckpt, time.time() - start_time))
return model
def _get_learning_rate_decay(self, hparams):
"""Get learning rate decay."""
if hparams.decay_scheme in ["luong5", "luong10", "luong234"]:
decay_factor = 0.5
if hparams.decay_scheme == "luong5":
start_decay_step = int(hparams.num_train_steps / 2)
decay_times = 5
elif hparams.decay_scheme == "luong10":
start_decay_step = int(hparams.num_train_steps / 2)
decay_times = 10
elif hparams.decay_scheme == "luong234":
start_decay_step = int(hparams.num_train_steps * 2 / 3)
decay_times = 4
remain_steps = hparams.num_train_steps - start_decay_step
decay_steps = int(remain_steps / decay_times)
elif not hparams.decay_scheme: # no decay
start_decay_step = hparams.num_train_steps
decay_steps = 0
decay_factor = 1.0
elif hparams.decay_scheme:
raise ValueError("Unknown decay scheme %s" % hparams.decay_scheme)
utils.print_out(
" decay_scheme=%s, start_decay_step=%d, decay_steps %d, "
"decay_factor %g" % (hparams.decay_scheme, start_decay_step,
decay_steps, decay_factor))
return tf.cond(self.global_step < start_decay_step,
lambda: self.learning_rate,
lambda: tf.train.exponential_decay(self.learning_rate, (
self.global_step - start_decay_step),
decay_steps,
decay_factor,
staircase=True),
name="learning_rate_decay_cond")
def decode_and_evaluate(name,
model,
sess,
trans_file,
ref_file,
metrics,
subword_option,
beam_width,
tgt_eos,
num_translations_per_input=1,
decode=True):
"""Decode a test set and compute a score according to the evaluation task."""
# Decode
if decode:
utils.print_out(" decoding to output %s." % trans_file)
start_time = time.time()
num_sentences = 0
with codecs.getwriter("utf-8")(
tf.gfile.GFile(trans_file, mode="wb")) as trans_f:
trans_f.write("") # Write empty string to ensure file is created.
num_translations_per_input = max(
min(num_translations_per_input, beam_width), 1)
while True:
try:
nmt_outputs, _ = model.decode(sess)
if beam_width == 0:
nmt_outputs = np.expand_dims(nmt_outputs, 0)
batch_size = nmt_outputs.shape[1]
num_sentences += batch_size
for sent_id in range(batch_size):
for beam_id in range(num_translations_per_input):
translation = get_translation(
nmt_outputs[beam_id],
sent_id,
tgt_eos=tgt_eos,
subword_option=subword_option)
trans_f.write((translation + b"\n").decode("utf-8"))
except tf.errors.OutOfRangeError:
utils.print_time(
" done, num sentences %d, num translations per input %d" %
(num_sentences, num_translations_per_input), start_time)
break
# Evaluation
evaluation_scores = {}
if ref_file and tf.gfile.Exists(trans_file):
for metric in metrics:
score = evaluation_utils.evaluate(
ref_file,
trans_file,
metric,
subword_option=subword_option)
evaluation_scores[metric] = score
utils.print_out(" %s %s: %.1f" % (metric, name, score))
return evaluation_scores
def _cell_list(unit_type,
num_units,
num_layers,
num_residual_layers,
forget_bias,
dropout,
mode,
num_gpus,
base_gpu=0,
single_cell_fn=None,
residual_fn=None):
"""Create a list of RNN cells."""
if not single_cell_fn:
single_cell_fn = _single_cell
# Multi-GPU
cell_list = []
for i in range(num_layers):
utils.print_out(" cell %d" % i, new_line=False)
single_cell = single_cell_fn(
unit_type=unit_type,
num_units=num_units,
forget_bias=forget_bias,
dropout=dropout,
mode=mode,
residual_connection=(i >= num_layers - num_residual_layers),
device_str=get_device_str(i + base_gpu, num_gpus),
residual_fn=residual_fn)
utils.print_out("")
cell_list.append(single_cell)
return cell_list
def _get_infer_maximum_iterations(self, hparams, source_sequence_length):
"""Maximum decoding steps at inference time."""
if hparams.tgt_max_len_infer:
maximum_iterations = hparams.tgt_max_len_infer
utils.print_out(" decoding maximum_iterations %d" %
maximum_iterations)
else:
# TODO(thangluong): add decoding_length_factor flag
decoding_length_factor = 2.0
max_encoder_length = tf.reduce_max(source_sequence_length)
maximum_iterations = tf.to_int32(
tf.round(
tf.to_float(max_encoder_length) * decoding_length_factor))
return maximum_iterations
def create_or_load_model(model, model_dir, session, name):
"""Create translation model and initialize or load parameters in session."""
latest_ckpt = tf.train.latest_checkpoint(model_dir)
if latest_ckpt:
model = load_model(model, latest_ckpt, session, name)
else:
start_time = time.time()
session.run(tf.global_variables_initializer())
session.run(tf.tables_initializer())
utils.print_out(
" created %s model with fresh parameters, time %.2fs" %
(name, time.time() - start_time))
global_step = model.global_step.eval(session=session)
return model, global_step
def build_graph(self, hparams, scope=None):
"""Subclass must implement this method.
Creates a sequence-to-sequence model with dynamic RNN decoder API.
Args:
hparams: Hyperparameter configurations.
scope: VariableScope for the created subgraph; default "dynamic_seq2seq".
Returns:
A tuple of the form (logits, loss, final_context_state, sample_id),
where:
logits: float32 Tensor [batch_size x num_decoder_symbols].
loss: the total loss / batch_size.
final_context_state: The final state of decoder RNN.
sample_id: the ids of decoder sequence
Raises:
ValueError: if encoder_type differs from mono and bi, or
attention_option is not (luong | scaled_luong |
bahdanau | normed_bahdanau).
"""
utils.print_out("# creating %s graph ..." % self.mode)
dtype = tf.float32
with tf.variable_scope(scope or "dynamic_seq2seq", dtype=dtype):
# Encoder
encoder_outputs, encoder_state = self._build_encoder(hparams)
## Decoder
logits, sample_id, final_context_state = self._build_decoder(
encoder_outputs, encoder_state, hparams)
## Loss infer 的时候不计算loss,提高计算速度
if self.mode != tf.contrib.learn.ModeKeys.INFER:
with tf.device(
model_helper.get_device_str(
self.num_encoder_layers - 1, self.num_gpus)):
loss = self._compute_loss(logits)
else:
loss = None
return logits, loss, final_context_state, sample_id
def _create_pretrained_emb_from_txt(vocab_file,
embed_file,
num_trainable_tokens=3,
dtype=tf.float32,
scope=None):
"""Load pretrain embeding from embed_file, and return an embedding matrix.
Args:
embed_file: Path to a Glove formated embedding txt file.
num_trainable_tokens: Make the first n tokens in the vocab file as trainable
variables. Default is 3, which is "<unk>", "<s>" and "</s>".
"""
vocab, _ = vocab_utils.load_vocab(vocab_file)
trainable_tokens = vocab[:num_trainable_tokens]
utils.print_out("# Using pretrained embedding: %s." % embed_file)
utils.print_out(" with trainable tokens: ")
emb_dict, emb_size = vocab_utils.load_embed_txt(embed_file)
for token in trainable_tokens:
utils.print_out(" %s" % token)
if token not in emb_dict:
emb_dict[token] = [0.0] * emb_size
emb_mat = np.array([emb_dict[token] for token in vocab],
dtype=dtype.as_numpy_dtype())
emb_mat = tf.constant(emb_mat)
emb_mat_const = tf.slice(emb_mat, [num_trainable_tokens, 0], [-1, -1])
with tf.variable_scope(scope or "pretrain_embeddings",
dtype=dtype) as scope:
with tf.device(_get_embed_device(num_trainable_tokens)):
emb_mat_var = tf.get_variable("emb_mat_var",
[num_trainable_tokens, emb_size])
return tf.concat([emb_mat_var, emb_mat_const], 0)
def _get_learning_rate_warmup(self, hparams):
"""Get learning rate warmup."""
warmup_steps = hparams.warmup_steps
warmup_scheme = hparams.warmup_scheme
utils.print_out(
" learning_rate=%g, warmup_steps=%d, warmup_scheme=%s" %
(hparams.learning_rate, warmup_steps, warmup_scheme))
# Apply inverse decay if global steps less than warmup steps.
# Inspired by https://arxiv.org/pdf/1706.03762.pdf (Section 5.3)
# When step < warmup_steps,
# learing_rate *= warmup_factor ** (warmup_steps - step)
if warmup_scheme == "t2t":
# 0.01^(1/warmup_steps): we start with a lr, 100 times smaller
warmup_factor = tf.exp(tf.log(0.01) / warmup_steps)
inv_decay = warmup_factor**(tf.to_float(warmup_steps -
self.global_step))
else:
raise ValueError("Unknown warmup scheme %s" % warmup_scheme)
return tf.cond(self.global_step < hparams.warmup_steps,
lambda: inv_decay * self.learning_rate,
lambda: self.learning_rate,
name="learning_rate_warump_cond")
def _build_encoder(self, hparams):
"""Build an encoder."""
num_layers = self.num_encoder_layers
num_residual_layers = self.num_encoder_residual_layers
iterator = self.iterator
source = iterator.source
if self.time_major:
source = tf.transpose(source)
with tf.variable_scope("encoder") as scope:
dtype = scope.dtype
# Look up embedding, emp_inp: [max_time, batch_size, num_units]
encoder_emb_inp = tf.nn.embedding_lookup(self.embedding_encoder,
source)
# Encoder_outputs: [max_time, batch_size, num_units]
if hparams.encoder_type == "uni":
utils.print_out(" num_layers = %d, num_residual_layers=%d" %
(num_layers, num_residual_layers))
cell = self._build_encoder_cell(hparams, num_layers,
num_residual_layers)
encoder_outputs, encoder_state = tf.nn.dynamic_rnn(
cell,
encoder_emb_inp,
dtype=dtype,
sequence_length=iterator.source_sequence_length,
time_major=self.time_major,
swap_memory=True)
elif hparams.encoder_type == "bi":
num_bi_layers = int(num_layers / 2)
num_bi_residual_layers = int(num_residual_layers / 2)
utils.print_out(
" num_bi_layers = %d, num_bi_residual_layers=%d" %
(num_bi_layers, num_bi_residual_layers))
encoder_outputs, bi_encoder_state = (
self._build_bidirectional_rnn(
inputs=encoder_emb_inp,
sequence_length=iterator.source_sequence_length,
dtype=dtype,
hparams=hparams,
num_bi_layers=num_bi_layers,
num_bi_residual_layers=num_bi_residual_layers))
if num_bi_layers == 1:
encoder_state = bi_encoder_state
else:
# alternatively concat forward and backward states
encoder_state = []
for layer_id in range(num_bi_layers):
encoder_state.append(
bi_encoder_state[0][layer_id]) # forward
encoder_state.append(
bi_encoder_state[1][layer_id]) # backward
encoder_state = tuple(encoder_state)
else:
raise ValueError("Unknown encoder_type %s" %
hparams.encoder_type)
return encoder_outputs, encoder_state
def __init__(self,
hparams,
mode,
iterator,
source_vocab_table,
target_vocab_table,
reverse_target_vocab_table=None,
scope=None,
extra_args=None):
"""Create the model.
Args:
hparams: Hyperparameter configurations.
mode: TRAIN | EVAL | INFER
iterator: Dataset Iterator that feeds data.
source_vocab_table: Lookup table mapping source words to ids.
target_vocab_table: Lookup table mapping target words to ids.
reverse_target_vocab_table: Lookup table mapping ids to target words. Only
required in INFER mode. Defaults to None.
scope: scope of the model.
extra_args: model_helper.ExtraArgs, for passing customizable functions.
"""
assert isinstance(iterator, iterator_utils.BatchedInput)
self.iterator = iterator
self.mode = mode
self.src_vocab_table = source_vocab_table
self.tgt_vocab_table = target_vocab_table
# source 词库大小
self.src_vocab_size = hparams.src_vocab_size
# target 词库大小
self.tgt_vocab_size = hparams.tgt_vocab_size
self.num_gpus = hparams.num_gpus
self.time_major = hparams.time_major
# extra_args: to make it flexible for adding external customizable code
self.single_cell_fn = None
if extra_args: # 单一的RNNs
self.single_cell_fn = extra_args.single_cell_fn
# Set num layers of encoder layer and decoder layer
self.num_encoder_layers = hparams.num_encoder_layers
self.num_decoder_layers = hparams.num_decoder_layers
assert self.num_encoder_layers
assert self.num_decoder_layers
# Set num residual layers 剩余？？？
if hasattr(hparams,
"num_residual_layers"): # compatible common_test_utils
self.num_encoder_residual_layers = hparams.num_residual_layers
self.num_decoder_residual_layers = hparams.num_residual_layers
else:
self.num_encoder_residual_layers = hparams.num_encoder_residual_layers
self.num_decoder_residual_layers = hparams.num_decoder_residual_layers
# Initializer 初始化随机种子等
initializer = model_helper.get_initializer(hparams.init_op,
hparams.random_seed,
hparams.init_weight)
tf.get_variable_scope().set_initializer(initializer)
# Embeddings 逻辑实现包含：加载预训练的词向量或者在图中加入embedding layer
self.init_embeddings(hparams, scope)
# batch_size
self.batch_size = tf.size(self.iterator.source_sequence_length)
# Projection 定义decoder层输出的投影层FC，进行向量维度转化
with tf.variable_scope(scope or "build_network"):
with tf.variable_scope("decoder/output_projection"):
self.output_layer = layers_core.Dense(hparams.tgt_vocab_size,
use_bias=False,
name="output_projection")
## Train graph build seq2seq model to train， 并且返回decoder结果
res = self.build_graph(
hparams, scope=scope) # (logits, loss, final_context_state)
# 如果是训练模式
if self.mode == tf.contrib.learn.ModeKeys.TRAIN:
self.train_loss = res[1]
self.word_count = tf.reduce_sum( # 总的词数量
self.iterator.source_sequence_length) + tf.reduce_sum(
self.iterator.target_sequence_length)
elif self.mode == tf.contrib.learn.ModeKeys.EVAL:
self.eval_loss = res[1]
elif self.mode == tf.contrib.learn.ModeKeys.INFER:
self.infer_logits, _, self.final_context_state, self.sample_id = res
# 将decoer得到的id结果转化为string 格式
self.sample_words = reverse_target_vocab_table.lookup(
tf.to_int64(self.sample_id))
if self.mode != tf.contrib.learn.ModeKeys.INFER:
## Count the number of predicted words for compute ppl.
self.predict_count = tf.reduce_sum(
self.iterator.target_sequence_length)
self.global_step = tf.Variable(0, trainable=False)
params = tf.trainable_variables()
# Gradients and SGD update operation for training the model.
# Arrage for the embedding vars to appear at the beginning.
if self.mode == tf.contrib.learn.ModeKeys.TRAIN:
self.learning_rate = tf.constant(hparams.learning_rate)
# warm-up
self.learning_rate = self._get_learning_rate_warmup(hparams)
# decay
self.learning_rate = self._get_learning_rate_decay(hparams)
# Optimizer
if hparams.optimizer == "sgd":
opt = tf.train.GradientDescentOptimizer(self.learning_rate)
tf.summary.scalar("lr", self.learning_rate)
elif hparams.optimizer == "adam":
opt = tf.train.AdamOptimizer(self.learning_rate)
# Gradients
gradients = tf.gradients(self.train_loss,
params,
colocate_gradients_with_ops=hparams.
colocate_gradients_with_ops)
# 梯度截断
clipped_grads, grad_norm_summary, grad_norm = model_helper.gradient_clip(
gradients, max_gradient_norm=hparams.max_gradient_norm)
self.grad_norm = grad_norm
self.update = opt.apply_gradients(zip(clipped_grads, params),
global_step=self.global_step)
# Summary
self.train_summary = tf.summary.merge([
tf.summary.scalar("lr", self.learning_rate),
tf.summary.scalar("train_loss", self.train_loss),
] + grad_norm_summary)
if self.mode == tf.contrib.learn.ModeKeys.INFER:
self.infer_summary = self._get_infer_summary(hparams)
# Saver
self.saver = tf.train.Saver(tf.global_variables(),
max_to_keep=hparams.num_keep_ckpts)
# Print trainable variables
utils.print_out("# Trainable variables")
for param in params:
utils.print_out(
" %s, %s, %s" %
(param.name, str(param.get_shape()), param.op.device))
def avg_checkpoints(model_dir, num_last_checkpoints, global_step,
global_step_name):
"""Average the last N checkpoints in the model_dir."""
checkpoint_state = tf.train.get_checkpoint_state(model_dir)
if not checkpoint_state:
utils.print_out("# No checkpoint file found in directory: %s" %
model_dir)
return None
# Checkpoints are ordered from oldest to newest.
checkpoints = (
checkpoint_state.all_model_checkpoint_paths[-num_last_checkpoints:])
if len(checkpoints) < num_last_checkpoints:
utils.print_out(
"# Skipping averaging checkpoints because not enough checkpoints is "
"avaliable.")
return None
avg_model_dir = os.path.join(model_dir, "avg_checkpoints")
if not tf.gfile.Exists(avg_model_dir):
utils.print_out(
"# Creating new directory %s for saving averaged checkpoints." %
avg_model_dir)
tf.gfile.MakeDirs(avg_model_dir)
utils.print_out("# Reading and averaging variables in checkpoints:")
var_list = tf.contrib.framework.list_variables(checkpoints[0])
var_values, var_dtypes = {}, {}
for (name, shape) in var_list:
if name != global_step_name:
var_values[name] = np.zeros(shape)
for checkpoint in checkpoints:
utils.print_out(" %s" % checkpoint)
reader = tf.contrib.framework.load_checkpoint(checkpoint)
for name in var_values:
tensor = reader.get_tensor(name)
var_dtypes[name] = tensor.dtype
var_values[name] += tensor
for name in var_values:
var_values[name] /= len(checkpoints)
# Build a graph with same variables in the checkpoints, and save the averaged
# variables into the avg_model_dir.
with tf.Graph().as_default():
tf_vars = [
tf.get_variable(v,
shape=var_values[v].shape,
dtype=var_dtypes[name]) for v in var_values
]
placeholders = [
tf.placeholder(v.dtype, shape=v.shape) for v in tf_vars
]
assign_ops = [tf.assign(v, p) for (v, p) in zip(tf_vars, placeholders)]
global_step_var = tf.Variable(global_step,
name=global_step_name,
trainable=False)
saver = tf.train.Saver(tf.all_variables())
with tf.Session() as sess:
sess.run(tf.initialize_all_variables())
for p, assign_op, (name, value) in zip(placeholders, assign_ops,
six.iteritems(var_values)):
sess.run(assign_op, {p: value})
# Use the built saver to save the averaged checkpoint. Only keep 1
# checkpoint and the best checkpoint will be moved to avg_best_metric_dir.
saver.save(sess, os.path.join(avg_model_dir, "translate.ckpt"))
return avg_model_dir
def _single_cell(unit_type,
num_units,
forget_bias,
dropout,
mode,
residual_connection=False,
device_str=None,
residual_fn=None):
"""Create an instance of a single RNN cell."""
# dropout (= 1 - keep_prob) is set to 0 during eval and infer
dropout = dropout if mode == tf.contrib.learn.ModeKeys.TRAIN else 0.0
# Cell Type
if unit_type == "lstm":
utils.print_out(" LSTM, forget_bias=%g" % forget_bias, new_line=False)
single_cell = tf.contrib.rnn.BasicLSTMCell(num_units,
forget_bias=forget_bias)
elif unit_type == "gru":
utils.print_out(" GRU", new_line=False)
single_cell = tf.contrib.rnn.GRUCell(num_units)
elif unit_type == "layer_norm_lstm":
utils.print_out(" Layer Normalized LSTM, forget_bias=%g" %
forget_bias,
new_line=False)
single_cell = tf.contrib.rnn.LayerNormBasicLSTMCell(
num_units, forget_bias=forget_bias, layer_norm=True)
elif unit_type == "nas":
utils.print_out(" NASCell", new_line=False)
single_cell = tf.contrib.rnn.NASCell(num_units)
else:
raise ValueError("Unknown unit type %s!" % unit_type)
# Dropout (= 1 - keep_prob)
if dropout > 0.0:
single_cell = tf.contrib.rnn.DropoutWrapper(cell=single_cell,
input_keep_prob=(1.0 -
dropout))
utils.print_out(" %s, dropout=%g " %
(type(single_cell).__name__, dropout),
new_line=False)
# Residual
if residual_connection:
single_cell = tf.contrib.rnn.ResidualWrapper(single_cell,
residual_fn=residual_fn)
utils.print_out(" %s" % type(single_cell).__name__, new_line=False)
# Device Wrapper
if device_str:
single_cell = tf.contrib.rnn.DeviceWrapper(single_cell, device_str)
utils.print_out(" %s, device=%s" %
(type(single_cell).__name__, device_str),
new_line=False)
return single_cell
def create_emb_for_encoder_and_decoder(share_vocab,
src_vocab_size,
tgt_vocab_size,
src_embed_size,
tgt_embed_size,
dtype=tf.float32,
num_partitions=0,
src_vocab_file=None,
tgt_vocab_file=None,
src_embed_file=None,
tgt_embed_file=None,
scope=None):
"""Create embedding matrix for both encoder and decoder.
Args:
share_vocab: A boolean. Whether to share embedding matrix for both
encoder and decoder.
src_vocab_size: An integer. The source vocab size.
tgt_vocab_size: An integer. The target vocab size.
src_embed_size: An integer. The embedding dimension for the encoder's
embedding.
tgt_embed_size: An integer. The embedding dimension for the decoder's
embedding.
dtype: dtype of the embedding matrix. Default to float32.
num_partitions: number of partitions used for the embedding vars.
scope: VariableScope for the created subgraph. Default to "embedding".
Returns:
embedding_encoder: Encoder's embedding matrix.
embedding_decoder: Decoder's embedding matrix.
Raises:
ValueError: if use share_vocab but source and target have different vocab
size.
"""
if num_partitions <= 1:
partitioner = None
else:
# Note: num_partitions > 1 is required for distributed training due to
# embedding_lookup tries to colocate single partition-ed embedding variable
# with lookup ops. This may cause embedding variables being placed on worker
# jobs.
partitioner = tf.fixed_size_partitioner(num_partitions)
if (src_embed_file or tgt_embed_file) and partitioner:
raise ValueError(
"Can't set num_partitions > 1 when using pretrained embedding")
with tf.variable_scope(scope or "embeddings",
dtype=dtype,
partitioner=partitioner) as scope:
# Share embedding
if share_vocab:
if src_vocab_size != tgt_vocab_size:
raise ValueError(
"Share embedding but different src/tgt vocab sizes"
" %d vs. %d" % (src_vocab_size, tgt_vocab_size))
assert src_embed_size == tgt_embed_size
utils.print_out("# Use the same embedding for source and target")
vocab_file = src_vocab_file or tgt_vocab_file
embed_file = src_embed_file or tgt_embed_file
embedding_encoder = _create_or_load_embed("embedding_share",
vocab_file, embed_file,
src_vocab_size,
src_embed_size, dtype)
embedding_decoder = embedding_encoder
else:
with tf.variable_scope("encoder", partitioner=partitioner):
embedding_encoder = _create_or_load_embed(
"embedding_encoder", src_vocab_file, src_embed_file,
src_vocab_size, src_embed_size, dtype)
with tf.variable_scope("decoder", partitioner=partitioner):
embedding_decoder = _create_or_load_embed(
"embedding_decoder", tgt_vocab_file, tgt_embed_file,
tgt_vocab_size, tgt_embed_size, dtype)
return embedding_encoder, embedding_decoder
def _build_encoder(self, hparams):
"""Build a GNMT encoder."""
# 编码使用的RNN类型, 单向LSTM or BiLSTM
if hparams.encoder_type == "uni" or hparams.encoder_type == "bi":
return super(GNMTModel, self)._build_encoder(hparams)
if hparams.encoder_type != "gnmt":
raise ValueError("Unknown encoder_type %s" % hparams.encoder_type)
# Build GNMT encoder.
# RNN层数
num_bi_layers = 1
#
num_uni_layers = self.num_encoder_layers - num_bi_layers
utils.print_out(" num_bi_layers = %d" % num_bi_layers)
utils.print_out(" num_uni_layers = %d" % num_uni_layers)
iterator = self.iterator
source = iterator.source
if self.time_major:
source = tf.transpose(source)
with tf.variable_scope("encoder") as scope:
dtype = scope.dtype
# Look up embedding, emp_inp: [max_time, batch_size, num_units]
# when time_major = True
# embedding look_up
encoder_emb_inp = tf.nn.embedding_lookup(self.embedding_encoder,
source)
# Execute _build_bidirectional_rnn from Model class
# BLSTM 用于输入编码
bi_encoder_outputs, bi_encoder_state = self._build_bidirectional_rnn(
inputs=encoder_emb_inp,
sequence_length=iterator.source_sequence_length,
dtype=dtype,
hparams=hparams,
num_bi_layers=num_bi_layers,
num_bi_residual_layers=0, # no residual connection
)
uni_cell = model_helper.create_rnn_cell(
unit_type=hparams.unit_type,
num_units=hparams.num_units,
num_layers=num_uni_layers,
num_residual_layers=self.num_encoder_residual_layers,
forget_bias=hparams.forget_bias,
dropout=hparams.dropout,
num_gpus=self.num_gpus,
base_gpu=1,
mode=self.mode,
single_cell_fn=self.single_cell_fn)
# encoder_outputs: size [max_time, batch_size, num_units]
# when time_major = True
# 使用LSTM 用于encoder
encoder_outputs, encoder_state = tf.nn.dynamic_rnn(
uni_cell,
bi_encoder_outputs,
dtype=dtype,
sequence_length=iterator.source_sequence_length,
time_major=self.time_major)
# Pass all encoder state except the first bi-directional layer's state to
# decoder. ？？？ why use first bi-lstm for input
encoder_state = (bi_encoder_state[1],) + (
(encoder_state,) if num_uni_layers == 1 else encoder_state)
return encoder_outputs, encoder_state
