基于TensorFlow2.0使用LSTM做机器翻译

import tensorflow as tf
import numpy as np
import unicodedata
import re

raw_data = (
    ('What a ridiculous concept!', 'Quel concept ridicule !'),
    ('Your idea is not entirely crazy.', "Votre idée n'est pas complètement folle."),
    ("A man's worth lies in what he is.", "La valeur d'un homme réside dans ce qu'il est."),
    ('What he did is very wrong.', "Ce qu'il a fait est très mal."),
    ("All three of you need to do that.", "Vous avez besoin de faire cela, tous les trois."),
    ("Are you giving me another chance?", "Me donnez-vous une autre chance ?"),
    ("Both Tom and Mary work as models.", "Tom et Mary travaillent tous les deux comme mannequins."),
    ("Can I have a few minutes, please?", "Puis-je avoir quelques minutes, je vous prie ?"),
    ("Could you close the door, please?", "Pourriez-vous fermer la porte, s'il vous plaît ?"),
    ("Did you plant pumpkins this year?", "Cette année, avez-vous planté des citrouilles ?"),
    ("Do you ever study in the library?", "Est-ce que vous étudiez à la bibliothèque des fois ?"),
    ("Don't be deceived by appearances.", "Ne vous laissez pas abuser par les apparences."),
    ("Excuse me. Can you speak English?", "Je vous prie de m'excuser ! Savez-vous parler anglais ?"),
    ("Few people know the true meaning.", "Peu de gens savent ce que cela veut réellement dire."),
    ("Germany produced many scientists.", "L'Allemagne a produit beaucoup de scientifiques."),
    ("Guess whose birthday it is today.", "Devine de qui c'est l'anniversaire, aujourd'hui !"),
    ("He acted like he owned the place.", "Il s'est comporté comme s'il possédait l'endroit."),
    ("Honesty will pay in the long run.", "L'honnêteté paye à la longue."),
    ("How do we know this isn't a trap?", "Comment savez-vous qu'il ne s'agit pas d'un piège ?"),
    ("I can't believe you're giving up.", "Je n'arrive pas à croire que vous abandonniez."),
)


def unicode_to_ascii(s):
    return ''.join(
        c for c in unicodedata.normalize('NFD', s)
        if unicodedata.category(c) != 'Mn')


def normalize_string(s):
    s = unicode_to_ascii(s)
    s = re.sub(r'([!.?])', r' \1', s)
    s = re.sub(r'[^a-zA-Z.!?]+', r' ', s)
    s = re.sub(r'\s+', r' ', s)
    return s


raw_data_en, raw_data_fr = list(zip(*raw_data))
raw_data_en, raw_data_fr = list(raw_data_en), list(raw_data_fr)
raw_data_en = [normalize_string(data) for data in raw_data_en]
raw_data_fr_in = [' ' + normalize_string(data) for data in raw_data_fr]
raw_data_fr_out = [normalize_string(data) + ' ' for data in raw_data_fr]

en_tokenizer = tf.keras.preprocessing.text.Tokenizer(filters='')
en_tokenizer.fit_on_texts(raw_data_en)
data_en = en_tokenizer.texts_to_sequences(raw_data_en)
data_en = tf.keras.preprocessing.sequence.pad_sequences(data_en,
                                                        padding='post')

fr_tokenizer = tf.keras.preprocessing.text.Tokenizer(filters='')
fr_tokenizer.fit_on_texts(raw_data_fr_in)
fr_tokenizer.fit_on_texts(raw_data_fr_out)
data_fr_in = fr_tokenizer.texts_to_sequences(raw_data_fr_in)
data_fr_in = tf.keras.preprocessing.sequence.pad_sequences(data_fr_in,
                                                           padding='post')

data_fr_out = fr_tokenizer.texts_to_sequences(raw_data_fr_out)
data_fr_out = tf.keras.preprocessing.sequence.pad_sequences(data_fr_out,
                                                            padding='post')

BATCH_SIZE = 5
dataset = tf.data.Dataset.from_tensor_slices(
    (data_en, data_fr_in, data_fr_out))
dataset = dataset.shuffle(20).batch(BATCH_SIZE)


class Encoder(tf.keras.Model):
    def __init__(self, vocab_size, embedding_size, lstm_size):
        super(Encoder, self).__init__()
        self.lstm_size = lstm_size
        self.embedding = tf.keras.layers.Embedding(vocab_size, embedding_size)
        self.lstm = tf.keras.layers.LSTM(
            lstm_size, return_sequences=True, return_state=True)

    def call(self, sequence, states):
        embed = self.embedding(sequence)
        output, state_h, state_c = self.lstm(embed, initial_state=states)

        return output, state_h, state_c

    def init_states(self, batch_size):
        return (tf.zeros([batch_size, self.lstm_size]),
                tf.zeros([batch_size, self.lstm_size]))


class Decoder(tf.keras.Model):
    def __init__(self, vocab_size, embedding_size, lstm_size):
        super(Decoder, self).__init__()
        self.lstm_size = lstm_size
        self.embedding = tf.keras.layers.Embedding(vocab_size, embedding_size)
        self.lstm = tf.keras.layers.LSTM(
            lstm_size, return_sequences=True, return_state=True)
        self.dense = tf.keras.layers.Dense(vocab_size)

    def call(self, sequence, state):
        embed = self.embedding(sequence)
        lstm_out, state_h, state_c = self.lstm(embed, state)
        logits = self.dense(lstm_out)

        return logits, state_h, state_c

    def init_states(self, batch_size):
        return (tf.zeros([batch_size, self.lstm_size]),
                tf.zeros([batch_size, self.lstm_size]))


en_vocab_size = len(en_tokenizer.word_index) + 1
fr_vocab_size = len(fr_tokenizer.word_index) + 1

EMBEDDING_SIZE = 32
LSTM_SIZE = 64

encoder = Encoder(en_vocab_size, EMBEDDING_SIZE, LSTM_SIZE)
decoder = Decoder(fr_vocab_size, EMBEDDING_SIZE, LSTM_SIZE)

initial_states = encoder.init_states(1)
encoder_outputs = encoder(tf.constant([[1, 2, 3]]), initial_states)
decoder_outputs = decoder(tf.constant([[1, 2, 3]]), encoder_outputs[1:])


def loss_func(targets, logits):
    crossentropy = tf.keras.losses.SparseCategoricalCrossentropy(
        from_logits=True)
    mask = tf.math.logical_not(tf.math.equal(targets, 0))
    mask = tf.cast(mask, dtype=tf.int64)
    loss = crossentropy(targets, logits, sample_weight=mask)

    return loss


optimizer = tf.keras.optimizers.Adam(lr=1e-3)


def predict(test_source_text=None):
    if test_source_text is None:
        test_source_text = raw_data_en[np.random.choice(len(raw_data_en))]
    print(test_source_text)
    test_source_seq = en_tokenizer.texts_to_sequences([test_source_text])
    print(test_source_seq)

    en_initial_states = encoder.init_states(1)
    en_outputs = encoder(tf.constant(test_source_seq), en_initial_states)

    de_input = tf.constant([[fr_tokenizer.word_index['']]])
    de_state_h, de_state_c = en_outputs[1:]
    out_words = []

    while True:
        de_output, de_state_h, de_state_c = decoder(
            de_input, (de_state_h, de_state_c))
        de_input = tf.argmax(de_output, -1)
        out_words.append(fr_tokenizer.index_word[de_input.numpy()[0][0]])

        if out_words[-1] == '' or len(out_words) >= 20:
            break

    print(' '.join(out_words))


@tf.function
def train_step(source_seq, target_seq_in, target_seq_out, en_initial_states):
    loss = 0
    with tf.GradientTape() as tape:
        en_outputs = encoder(source_seq, en_initial_states)
        en_states = en_outputs[1:]
        de_states = en_states

        de_outputs = decoder(target_seq_in, de_states)
        logits = de_outputs[0]
        loss = loss_func(target_seq_out, logits)

    variables = encoder.trainable_variables + decoder.trainable_variables
    gradients = tape.gradient(loss, variables)
    optimizer.apply_gradients(zip(gradients, variables))

    return loss


NUM_EPOCHS = 300

for e in range(NUM_EPOCHS):
    en_initial_states = encoder.init_states(BATCH_SIZE)

    predict()

    for batch, (source_seq, target_seq_in, target_seq_out) in enumerate(dataset.take(-1)):
        loss = train_step(source_seq, target_seq_in,
                          target_seq_out, en_initial_states)

    print('Epoch {} Loss {:.4f}'.format(e + 1, loss.numpy()))

test_sents = (
    'What a ridiculous concept!',
    'Your idea is not entirely crazy.',
    "A man's worth lies in what he is.",
    'What he did is very wrong.',
    "All three of you need to do that.",
    "Are you giving me another chance?",
    "Both Tom and Mary work as models.",
    "Can I have a few minutes, please?",
    "Could you close the door, please?",
    "Did you plant pumpkins this year?",
    "Do you ever study in the library?",
    "Don't be deceived by appearances.",
    "Excuse me. Can you speak English?",
    "Few people know the true meaning.",
    "Germany produced many scientists.",
    "Guess whose birthday it is today.",
    "He acted like he owned the place.",
    "Honesty will pay in the long run.",
    "How do we know this isn't a trap?",
    "I can't believe you're giving up.",
)

for test_sent in test_sents:
    test_sequence = normalize_string(test_sent)
    predict(test_sequence)

参考：
LSTM机器翻译详解