基于Pytorch框架的深度学习语言对话模型

首先声明！！！

---

• 1、脚本为本人总结，如有使用注明出处。
• 2、模型基于Pytorch框架实现及训练。
• 3、脚本内有注释。

---

运行过程：

对话截图：

Seq2Seq模型源码：

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import time
import torch
import torch.nn as nn
from torch import optim
import torch.nn.functional as F
import csv
import random
import re
import os
import unicodedata
import codecs
from io import open
import itertools


USE_CUDA = torch.cuda.is_available()
device = 'cpu'


start_time = time.time()
corpus_name = "cornell movie-dialogs corpus"
corpus = os.path.join("./", corpus_name)


def printLines(file, n=10):
    with open(file, 'rb') as datafile:
        lines = datafile.readlines()
    for line in lines[:n]:
        print(line)

printLines(os.path.join(corpus, "movie_lines.txt"))


# 把每一行都parse成一个dict，key是lineID、characterID、movieID、character和text
# 分别代表这一行的ID、人物ID、电影ID，人物名称和文本。
# 最终输出一个dict，key是lineID，value是一个dict。
# value这个dict的key是lineID、characterID、movieID、character和text
def loadLines(fileName, fields):
    lines = {}
    print(os.path.join(corpus, "movie_lines.txt"))
    with open(fileName, 'r', encoding='iso-8859-1') as f:
        for line in f:
            values = line.split(" +++$+++ ")
            # 抽取fields
            lineObj = {}
            for i, field in enumerate(fields):
                lineObj[field] = values[i]
            lines[lineObj['lineID']] = lineObj
    return lines


# 根据movie_conversations.txt文件和上输出的lines，把utterance组成对话。
# 最终输出一个list，这个list的每一个元素都是一个dict，
# key分别是character1ID、character2ID、movieID和utteranceIDs。
# 分别表示这对话的第一个人物的ID，第二个的ID，电影的ID以及它包含的utteranceIDs
# 最后根据lines，还给每一行的dict增加一个key为lines，其value是个list，
# 包含所有utterance(上面得到的lines的value)
def loadConversations(fileName, lines, fields):
    conversations = []
    with open(fileName, 'r', encoding='iso-8859-1') as f:
        for line in f:
            values = line.split(" +++$+++ ")
            # 抽取fields
            convObj = {}
            for i, field in enumerate(fields):
                convObj[field] = values[i]
            # convObj["utteranceIDs"]是一个字符串，形如['L198', 'L199']
            # 我们用eval把这个字符串变成一个字符串的list。
            lineIds = eval(convObj["utteranceIDs"])
            # 根据lineIds构造一个数组，根据lineId去lines里检索出存储utterance对象。
            convObj["lines"] = []
            for lineId in lineIds:
                convObj["lines"].append(lines[lineId])
            conversations.append(convObj)
    return conversations


# 从对话中抽取句对
# 假设一段对话包含s1,s2,s3,s4这4个utterance
# 那么会返回3个句对：s1-s2,s2-s3和s3-s4。
def extractSentencePairs(conversations):
    qa_pairs = []
    for conversation in conversations:
        # 遍历对话中的每一个句子，忽略最后一个句子，因为没有答案。
        for i in range(len(conversation["lines"]) - 1):
            inputLine = conversation["lines"][i]["text"].strip()
            targetLine = conversation["lines"][i+1]["text"].strip()
            # 如果有空的句子就去掉
            if inputLine and targetLine:
                qa_pairs.append([inputLine, targetLine])
    return qa_pairs


# 定义新的文件
datafile = os.path.join(corpus, "formatted_movie_lines.txt")

delimiter = '\t'
# 对分隔符delimiter进行decode，这里对tab进行decode结果并没有变
delimiter = str(codecs.decode(delimiter, "unicode_escape"))

# 初始化dict lines，list conversations以及前面我们介绍过的field的id数组。
lines = {}
conversations = []
MOVIE_LINES_FIELDS = ["lineID", "characterID", "movieID", "character", "text"]
MOVIE_CONVERSATIONS_FIELDS = ["character1ID", "character2ID", "movieID", "utteranceIDs"]

# 首先使用loadLines函数处理movie_lines.txt
print("\nProcessing corpus...")
lines = loadLines(os.path.join(corpus, "movie_lines.txt"), MOVIE_LINES_FIELDS)
# 接着使用loadConversations处理上一步的结果，得到conversations
print("\nLoading conversations...")
conversations = loadConversations(os.path.join(corpus, "movie_conversations.txt"),
                                  lines, MOVIE_CONVERSATIONS_FIELDS)

# 输出到一个新的csv文件
print("\nWriting newly formatted file...")
with open(datafile, 'w', encoding='utf-8') as outputfile:
    writer = csv.writer(outputfile, delimiter=delimiter, lineterminator='\n')
    # 使用extractSentencePairs从conversations里抽取句对。
    for pair in extractSentencePairs(conversations):
        writer.writerow(pair)

# 输出一些行用于检查
print("\nSample lines from file:")
printLines(datafile)

# 预定义的token
PAD_token = 0  # 表示padding
SOS_token = 1  # 句子的开始
EOS_token = 2  # 句子的结束


class Voc:
    def __init__(self, name):
        self.name = name
        self.trimmed = False
        self.word2index = {}
        self.word2count = {}
        self.index2word = {PAD_token: "PAD", SOS_token: "SOS", EOS_token: "EOS"}
        self.num_words = 3  # 目前有SOS, EOS, PAD这3个token。

    def addSentence(self, sentence):
        for word in sentence.split(' '):
            self.addWord(word)

    def addWord(self, word):
        if word not in self.word2index:
            self.word2index[word] = self.num_words
            self.word2count[word] = 1
            self.index2word[self.num_words] = word
            self.num_words += 1
        else:
            self.word2count[word] += 1

    # 删除频次小于min_count的token
    def trim(self, min_count):
        if self.trimmed:
            return
        self.trimmed = True

        keep_words = []

        for k, v in self.word2count.items():
            if v >= min_count:
                keep_words.append(k)

        print('keep_words {} / {} = {:.4f}'.format(
            len(keep_words), len(self.word2index), len(keep_words) / len(self.word2index)
        ))

        # 重新构造词典
        self.word2index = {}
        self.word2count = {}
        self.index2word = {PAD_token: "PAD", SOS_token: "SOS", EOS_token: "EOS"}
        self.num_words = 3  # Count default tokens

        # 重新构造后词频就没有意义了(都是1)
        for word in keep_words:
            self.addWord(word)


MAX_LENGTH = 10  # 句子最大长度是10个词(包括EOS等特殊词)


# 把Unicode字符串变成ASCII
# 参考https://stackoverflow.com/a/518232/2809427
def unicodeToAscii(s):
    return ''.join(
        c for c in unicodedata.normalize('NFD', s)
        if unicodedata.category(c) != 'Mn'
    )


def normalizeString(s):
    # 变成小写、去掉前后空格，然后unicode变成ascii
    s = unicodeToAscii(s.lower().strip())
    # 在标点前增加空格，这样把标点当成一个词
    s = re.sub(r"([.!?])", r" \1", s)
    # 字母和标点之外的字符都变成空格
    s = re.sub(r"[^a-zA-Z.!?]+", r" ", s)
    # 因为把不用的字符都变成空格，所以可能存在多个连续空格
    # 下面的正则替换把多个空格变成一个空格，最后去掉前后空格
    s = re.sub(r"\s+", r" ", s).strip()
    return s


# 读取问答句对并且返回Voc词典对象
def readVocs(datafile, corpus_name):
    print("Reading lines...")
    # 文件每行读取到list lines中。
    lines = open(datafile, encoding='utf-8'). \
        read().strip().split('\n')
    # 每行用tab切分成问答两个句子，然后调用normalizeString函数进行处理。
    pairs = [[normalizeString(s) for s in l.split('\t')] for l in lines]
    voc = Voc(corpus_name)
    return voc, pairs


def filterPair(p):
    return len(p[0].split(' ')) < MAX_LENGTH and len(p[1].split(' ')) < MAX_LENGTH


# 过滤太长的句对
def filterPairs(pairs):
    return [pair for pair in pairs if filterPair(pair)]


# 使用上面的函数进行处理，返回Voc对象和句对的list
def loadPrepareData(corpus, corpus_name, datafile):
    print("Start preparing training data ...")
    voc, pairs = readVocs(datafile, corpus_name)
    print("Read {!s} sentence pairs".format(len(pairs)))
    pairs = filterPairs(pairs)
    print("Trimmed to {!s} sentence pairs".format(len(pairs)))
    print("Counting words...")
    for pair in pairs:
        voc.addSentence(pair[0])
        voc.addSentence(pair[1])
    print("Counted words:", voc.num_words)
    return voc, pairs


# Load/Assemble voc and pairs
# save_dir = os.path.join("data", "save")
voc, pairs = loadPrepareData(corpus, corpus_name, datafile)
# 输出一些句对
print("\npairs:")
for pair in pairs[:10]:
    print(pair)


MIN_COUNT = 3    # 阈值为3


def trimRareWords(voc, pairs, MIN_COUNT):
    # 去掉voc中频次小于3的词
    voc.trim(MIN_COUNT)
    # 保留的句对
    keep_pairs = []
    for pair in pairs:
        input_sentence = pair[0]
        output_sentence = pair[1]
        keep_input = True
        keep_output = True
        # 检查问题
        for word in input_sentence.split(' '):
            if word not in voc.word2index:
                keep_input = False
                break
        # 检查答案
        for word in output_sentence.split(' '):
            if word not in voc.word2index:
                keep_output = False
                break

        # 如果问题和答案都只包含高频词，我们才保留这个句对
        if keep_input and keep_output:
            keep_pairs.append(pair)

    print("Trimmed from {} pairs to {}, {:.4f} of total".format(len(pairs),
		len(keep_pairs), len(keep_pairs) / len(pairs)))
    return keep_pairs


# 实际进行处理
pairs = trimRareWords(voc, pairs, MIN_COUNT)



# 把句子的词变成ID
def indexesFromSentence(voc, sentence):
    return [voc.word2index[word] for word in sentence.split(' ')] + [EOS_token]

# l是多个长度不同句子(list)，使用zip_longest padding成定长，长度为最长句子的长度。
def zeroPadding(l, fillvalue=PAD_token):
    return list(itertools.zip_longest(*l, fillvalue=fillvalue))

# l是二维的padding后的list
# 返回m和l的大小一样，如果某个位置是padding，那么值为0，否则为1
def binaryMatrix(l, value=PAD_token):
    m = []
    for i, seq in enumerate(l):
        m.append([])
        for token in seq:
            if token == PAD_token:
                m[i].append(0)
            else:
                m[i].append(1)
    return m

# 把输入句子变成ID，然后再padding，同时返回lengths这个list，标识实际长度。
# 返回的padVar是一个LongTensor，shape是(batch, max_length)，
# lengths是一个list，长度为(batch,)，表示每个句子的实际长度。
def inputVar(l, voc):
    indexes_batch = [indexesFromSentence(voc, sentence) for sentence in l]
    lengths = torch.tensor([len(indexes) for indexes in indexes_batch])
    padList = zeroPadding(indexes_batch)
    padVar = torch.LongTensor(padList)
    return padVar, lengths

# 对输出句子进行padding，然后用binaryMatrix得到每个位置是padding(0)还是非padding，
# 同时返回最大最长句子的长度(也就是padding后的长度)
# 返回值padVar是LongTensor，shape是(batch, max_target_length)
# mask是ByteTensor，shape也是(batch, max_target_length)
def outputVar(l, voc):
    indexes_batch = [indexesFromSentence(voc, sentence) for sentence in l]
    max_target_len = max([len(indexes) for indexes in indexes_batch])
    padList = zeroPadding(indexes_batch)
    mask = binaryMatrix(padList)
    mask = torch.ByteTensor(mask)
    padVar = torch.LongTensor(padList)
    return padVar, mask, max_target_len

# 处理一个batch的pair句对
def batch2TrainData(voc, pair_batch):
    # 按照句子的长度(词数)排序
    pair_batch.sort(key=lambda x: len(x[0].split(" ")), reverse=True)
    input_batch, output_batch = [], []
    for pair in pair_batch:
        input_batch.append(pair[0])
        output_batch.append(pair[1])
    inp, lengths = inputVar(input_batch, voc)
    output, mask, max_target_len = outputVar(output_batch, voc)
    return inp, lengths, output, mask, max_target_len


# 示例
small_batch_size = 5
batches = batch2TrainData(voc, [random.choice(pairs) for _ in range(small_batch_size)])
input_variable, lengths, target_variable, mask, max_target_len = batches

print("input_variable:", input_variable)
print("lengths:", lengths)
print("target_variable:", target_variable)
print("mask:", mask)
print("max_target_len:", max_target_len)


class EncoderRNN(nn.Module):
    def __init__(self, hidden_size, embedding, n_layers=1, dropout=0):
        super(EncoderRNN, self).__init__()
        self.n_layers = n_layers
        self.hidden_size = hidden_size
        self.embedding = embedding

        # 初始化GRU，这里输入和hidden大小都是hidden_size，这里假设embedding层的输出大小是hidden_size
        # 如果只有一层，那么不进行Dropout，否则使用传入的参数dropout进行GRU的Dropout。
        self.gru = nn.GRU(hidden_size, hidden_size, n_layers,
                          dropout=(0 if n_layers == 1 else dropout), bidirectional=True)

    def forward(self, input_seq, input_lengths, hidden=None):
        # 输入是(max_length, batch)，Embedding之后变成(max_length, batch, hidden_size)
        embedded = self.embedding(input_seq)
        # Pack padded batch of sequences for RNN module
        # 因为RNN(GRU)要知道实际长度，所以PyTorch提供了函数pack_padded_sequence把输入向量和长度
        # pack到一个对象PackedSequence里，这样便于使用。
        packed = torch.nn.utils.rnn.pack_padded_sequence(embedded, input_lengths)
        # 通过GRU进行forward计算，需要传入输入和隐变量
        # 如果传入的输入是一个Tensor (max_length, batch, hidden_size)
        # 那么输出outputs是(max_length, batch, hidden_size*num_directions)。
        # 第三维是hidden_size和num_directions的混合，它们实际排列顺序是num_directions在前面，
        # 因此我们可以使用outputs.view(seq_len, batch, num_directions, hidden_size)得到4维的向量。
        # 其中第三维是方向，第四位是隐状态。

        # 而如果输入是PackedSequence对象，那么输出outputs也是一个PackedSequence对象，我们需要用
        # 函数pad_packed_sequence把它变成shape为(max_length, batch, hidden*num_directions)的向量以及
        # 一个list，表示输出的长度，当然这个list和输入的input_lengths完全一样，因此通常我们不需要它。
        outputs, hidden = self.gru(packed, hidden)
        # 参考前面的注释，我们得到outputs为(max_length, batch, hidden*num_directions)
        outputs, _ = torch.nn.utils.rnn.pad_packed_sequence(outputs)
        # 我们需要把输出的num_directions双向的向量加起来
        # 因为outputs的第三维是先放前向的hidden_size个结果，然后再放后向的hidden_size个结果
        # 所以outputs[:, :, :self.hidden_size]得到前向的结果
        # outputs[:, :, self.hidden_size:]是后向的结果
        # 注意，如果bidirectional是False，则outputs第三维的大小就是hidden_size，
        # 这时outputs[:, : ,self.hidden_size:]是不存在的，因此也不会加上去。
        # 对Python slicing不熟的读者可以看看下面的例子：

        # >>> a=[1,2,3]
        # >>> a[:3]
        # [1, 2, 3]
        # >>> a[3:]
        # []
        # >>> a[:3]+a[3:]
        # [1, 2, 3]

        # 这样就不用写下面的代码了：
        # if bidirectional:
        #     outputs = outputs[:, :, :self.hidden_size] + outputs[:, : ,self.hidden_size:]
        outputs = outputs[:, :, :self.hidden_size] + outputs[:, :, self.hidden_size:]
        # 返回最终的输出和最后时刻的隐状态。
        return outputs, hidden


# Luong 注意力layer
class Attn(torch.nn.Module):
    def __init__(self, method, hidden_size):
        super(Attn, self).__init__()
        self.method = method
        if self.method not in ['dot', 'general', 'concat']:
            raise ValueError(self.method, "is not an appropriate attention method.")
        self.hidden_size = hidden_size
        if self.method == 'general':
            self.attn = torch.nn.Linear(self.hidden_size, hidden_size)
        elif self.method == 'concat':
            self.attn = torch.nn.Linear(self.hidden_size * 2, hidden_size)
            self.v = torch.nn.Parameter(torch.FloatTensor(hidden_size))

    def dot_score(self, hidden, encoder_output):
        # 输入hidden的shape是(1, batch=64, hidden_size=500)
        # encoder_outputs的shape是(input_lengths=10, batch=64, hidden_size=500)
        # hidden * encoder_output得到的shape是(10, 64, 500)，然后对第3维求和就可以计算出score。
        return torch.sum(hidden * encoder_output, dim=2)

    def general_score(self, hidden, encoder_output):
        energy = self.attn(encoder_output)
        return torch.sum(hidden * energy, dim=2)

    def concat_score(self, hidden, encoder_output):
        energy = self.attn(torch.cat((hidden.expand(encoder_output.size(0), -1, -1),
                                      encoder_output), 2)).tanh()
        return torch.sum(self.v * energy, dim=2)

    # 输入是上一个时刻的隐状态hidden和所有时刻的Encoder的输出encoder_outputs
    # 输出是注意力的概率，也就是长度为input_lengths的向量，它的和加起来是1。
    def forward(self, hidden, encoder_outputs):
        # 计算注意力的score，输入hidden的shape是(1, batch=64, hidden_size=500)，
        # 表示t时刻batch数据的隐状态
        # encoder_outputs的shape是(input_lengths=10, batch=64, hidden_size=500)
        if self.method == 'general':
            attn_energies = self.general_score(hidden, encoder_outputs)
        elif self.method == 'concat':
            attn_energies = self.concat_score(hidden, encoder_outputs)
        elif self.method == 'dot':
            # 计算内积，参考dot_score函数
            attn_energies = self.dot_score(hidden, encoder_outputs)

        # Transpose max_length and batch_size dimensions
        # 把attn_energies从(max_length=10, batch=64)转置成(64, 10)
        attn_energies = attn_energies.t()

        # 使用softmax函数把score变成概率，shape仍然是(64, 10)，然后用unsqueeze(1)变成
        # (64, 1, 10)
        return F.softmax(attn_energies, dim=1).unsqueeze(1)


class LuongAttnDecoderRNN(nn.Module):
    def __init__(self, attn_model, embedding, hidden_size, output_size, n_layers=1, dropout=0.1):
        super(LuongAttnDecoderRNN, self).__init__()

        # 保存到self里，attn_model就是前面定义的Attn类的对象。
        self.attn_model = attn_model
        self.hidden_size = hidden_size
        self.output_size = output_size
        self.n_layers = n_layers
        self.dropout = dropout

        # 定义Decoder的layers
        self.embedding = embedding
        self.embedding_dropout = nn.Dropout(dropout)
        self.gru = nn.GRU(hidden_size, hidden_size, n_layers, dropout=(0 if n_layers == 1 else dropout))
        self.concat = nn.Linear(hidden_size * 2, hidden_size)
        self.out = nn.Linear(hidden_size, output_size)

        self.attn = Attn(attn_model, hidden_size)

    def forward(self, input_step, last_hidden, encoder_outputs):
        # 注意：decoder每一步只能处理一个时刻的数据，因为t时刻计算完了才能计算t+1时刻。
        # input_step的shape是(1, 64)，64是batch，1是当前输入的词ID(来自上一个时刻的输出)
        # 通过embedding层变成(1, 64, 500)，然后进行dropout，shape不变。
        embedded = self.embedding(input_step)
        embedded = self.embedding_dropout(embedded)
        # 把embedded传入GRU进行forward计算
        # 得到rnn_output的shape是(1, 64, 500)
        # hidden是(2, 64, 500)，因为是两层的GRU，所以第一维是2。
        rnn_output, hidden = self.gru(embedded, last_hidden)
        # 计算注意力权重， 根据前面的分析，attn_weights的shape是(64, 1, 10)
        attn_weights = self.attn(rnn_output, encoder_outputs)

        # encoder_outputs是(10, 64, 500)
        # encoder_outputs.transpose(0, 1)后的shape是(64, 10, 500)
        # attn_weights.bmm后是(64, 1, 500)

        # bmm是批量的矩阵乘法，第一维是batch，我们可以把attn_weights看成64个(1,10)的矩阵
        # 把encoder_outputs.transpose(0, 1)看成64个(10, 500)的矩阵
        # 那么bmm就是64个(1, 10)矩阵 x (10, 500)矩阵，最终得到(64, 1, 500)
        context = attn_weights.bmm(encoder_outputs.transpose(0, 1))
        # 把context向量和GRU的输出拼接起来
        # rnn_output从(1, 64, 500)变成(64, 500)
        rnn_output = rnn_output.squeeze(0)
        # context从(64, 1, 500)变成(64, 500)
        context = context.squeeze(1)
        # 拼接得到(64, 1000)
        concat_input = torch.cat((rnn_output, context), 1)
        # self.concat是一个矩阵(1000, 500)，
        # self.concat(concat_input)的输出是(64, 500)
        # 然后用tanh把输出返回变成(-1,1)，concat_output的shape是(64, 500)
        concat_output = torch.tanh(self.concat(concat_input))

        # out是(500, 词典大小=7826)
        output = self.out(concat_output)
        # 用softmax变成概率，表示当前时刻输出每个词的概率。
        output = F.softmax(output, dim=1)
        # 返回 output和新的隐状态
        return output, hidden


def maskNLLLoss(inp, target, mask):
    # 计算实际的词的个数，因为padding是0，非padding是1，因此sum就可以得到词的个数
    nTotal = mask.sum()

    crossEntropy = -torch.log(torch.gather(inp, 1, target.view(-1, 1)).squeeze(1))
    loss = crossEntropy.masked_select(mask).mean()
    loss = loss.to(device)
    return loss, nTotal.item()


def train(input_variable, lengths, target_variable, mask, max_target_len, encoder, decoder, embedding,
          encoder_optimizer, decoder_optimizer, batch_size, clip, max_length=MAX_LENGTH):

    # 梯度清空
    encoder_optimizer.zero_grad()
    decoder_optimizer.zero_grad()

    # 设置device，从而支持GPU，当然如果没有GPU也能工作。
    input_variable = input_variable.to(device)
    lengths = lengths.to(device)
    target_variable = target_variable.to(device)
    mask = mask.to(device)

    # 初始化变量
    loss = 0
    print_losses = []
    n_totals = 0

    # encoder的Forward计算
    encoder_outputs, encoder_hidden = encoder(input_variable, lengths)

    # Decoder的初始输入是SOS，我们需要构造(1, batch)的输入，表示第一个时刻batch个输入。
    decoder_input = torch.LongTensor([[SOS_token for _ in range(batch_size)]])
    decoder_input = decoder_input.to(device)

    # 注意：Encoder是双向的，而Decoder是单向的，因此从下往上取n_layers个
    decoder_hidden = encoder_hidden[:decoder.n_layers]

    # 确定是否teacher forcing
    use_teacher_forcing = True if random.random() < teacher_forcing_ratio else False

    # 一次处理一个时刻
    if use_teacher_forcing:
        for t in range(max_target_len):
            decoder_output, decoder_hidden = decoder(
                decoder_input, decoder_hidden, encoder_outputs
            )
            # Teacher forcing: 下一个时刻的输入是当前正确答案
            decoder_input = target_variable[t].view(1, -1)
            # 计算累计的loss
            mask_loss, nTotal = maskNLLLoss(decoder_output, target_variable[t], mask[t])
            loss += mask_loss
            print_losses.append(mask_loss.item() * nTotal)
            n_totals += nTotal
    else:
        for t in range(max_target_len):
            decoder_output, decoder_hidden = decoder(
                decoder_input, decoder_hidden, encoder_outputs
            )
            # 不是teacher forcing: 下一个时刻的输入是当前模型预测概率最高的值
            _, topi = decoder_output.topk(1)
            decoder_input = torch.LongTensor([[topi[i][0] for i in range(batch_size)]])
            decoder_input = decoder_input.to(device)
            # 计算累计的loss
            mask_loss, nTotal = maskNLLLoss(decoder_output, target_variable[t], mask[t])
            loss += mask_loss
            print_losses.append(mask_loss.item() * nTotal)
            n_totals += nTotal

    # 反向计算
    loss.backward()

    # 对encoder和decoder进行梯度裁剪
    _ = torch.nn.utils.clip_grad_norm_(encoder.parameters(), clip)
    _ = torch.nn.utils.clip_grad_norm_(decoder.parameters(), clip)

    # 更新参数
    encoder_optimizer.step()
    decoder_optimizer.step()

    return sum(print_losses) / n_totals


def trainIters(model_name, voc, pairs, encoder, decoder, encoder_optimizer, decoder_optimizer,
               embedding, encoder_n_layers, decoder_n_layers, save_dir, n_iteration, batch_size,
               print_every, save_every, clip, corpus_name, loadFilename):
    # 随机选择n_iteration个batch的数据(pair)
    training_batches = [batch2TrainData(voc, [random.choice(pairs) for _ in range(batch_size)])
                        for _ in range(n_iteration)]

    # 初始化
    print('Initializing ...')
    start_iteration = 1
    print_loss = 0
    if loadFilename:
        start_iteration = checkpoint['iteration'] + 1

    # 训练
    print("Training...")
    for iteration in range(start_iteration, n_iteration + 1):
        training_batch = training_batches[iteration - 1]

        input_variable, lengths, target_variable, mask, max_target_len = training_batch

        # 训练一个batch的数据
        loss = train(input_variable, lengths, target_variable, mask, max_target_len, encoder,
                     decoder, embedding, encoder_optimizer, decoder_optimizer, batch_size, clip)
        print_loss += loss

        # 进度
        if iteration % print_every == 0:
            print_loss_avg = print_loss / print_every
            print("Iteration: {}; Percent complete: {:.1f}%; Average loss: {:.4f}"
                  .format(iteration, iteration / n_iteration * 100, print_loss_avg))
            print_loss = 0

        # 保存checkpoint
        if (iteration % save_every == 0):
            directory = os.path.join(save_dir, model_name, corpus_name, '{}-{}_{}'
                                     .format(encoder_n_layers, decoder_n_layers, hidden_size))
            if not os.path.exists(directory):
                os.makedirs(directory)
            torch.save({
                'iteration': iteration,
                'en': encoder.state_dict(),
                'de': decoder.state_dict(),
                'en_opt': encoder_optimizer.state_dict(),
                'de_opt': decoder_optimizer.state_dict(),
                'loss': loss,
                'voc_dict': voc.__dict__,
                'embedding': embedding.state_dict()
            }, os.path.join(directory, '{}_{}.tar'.format(iteration, 'checkpoint')))


class GreedySearchDecoder(nn.Module):
    def __init__(self, encoder, decoder):
        super(GreedySearchDecoder, self).__init__()
        self.encoder = encoder
        self.decoder = decoder

    def forward(self, input_seq, input_length, max_length):
        # Encoder的Forward计算
        encoder_outputs, encoder_hidden = self.encoder(input_seq, input_length)
        # 把Encoder最后时刻的隐状态作为Decoder的初始值
        decoder_hidden = encoder_hidden[:decoder.n_layers]
        # 因为我们的函数都是要求(time,batch)，因此即使只有一个数据，也要做出二维的。
        # Decoder的初始输入是SOS
        decoder_input = torch.ones(1, 1, device=device, dtype=torch.long) * SOS_token
        # 用于保存解码结果的tensor
        all_tokens = torch.zeros([0], device=device, dtype=torch.long)
        all_scores = torch.zeros([0], device=device)
        # 循环，这里只使用长度限制，后面处理的时候把EOS去掉了。
        for _ in range(max_length):
            # Decoder forward一步
            decoder_output, decoder_hidden = self.decoder(decoder_input, decoder_hidden,
								encoder_outputs)
            # decoder_outputs是(batch=1, vob_size)
            # 使用max返回概率最大的词和得分
            decoder_scores, decoder_input = torch.max(decoder_output, dim=1)
            # 把解码结果保存到all_tokens和all_scores里
            all_tokens = torch.cat((all_tokens, decoder_input), dim=0)
            all_scores = torch.cat((all_scores, decoder_scores), dim=0)
            # decoder_input是当前时刻输出的词的ID，这是个一维的向量，因为max会减少一维。
            # 但是decoder要求有一个batch维度，因此用unsqueeze增加batch维度。
            decoder_input = torch.unsqueeze(decoder_input, 0)
        # 返回所有的词和得分。
        return all_tokens, all_scores


def evaluate(encoder, decoder, searcher, voc, sentence, max_length=MAX_LENGTH):
    ### 把输入的一个batch句子变成id
    indexes_batch = [indexesFromSentence(voc, sentence)]
    # 创建lengths tensor
    lengths = torch.tensor([len(indexes) for indexes in indexes_batch])
    # 转置
    input_batch = torch.LongTensor(indexes_batch).transpose(0, 1)
    # 放到合适的设备上(比如GPU)
    input_batch = input_batch.to(device)
    lengths = lengths.to(device)
    # 用searcher解码
    tokens, scores = searcher(input_batch, lengths, max_length)
    # ID变成词。
    decoded_words = [voc.index2word[token.item()] for token in tokens]
    return decoded_words


def evaluateInput(encoder, decoder, searcher, voc):
    input_sentence = ''
    while (1):
        try:
            # 得到用户终端的输入
            input_sentence = input('> ')
            # 是否退出
            if input_sentence == 'q' or input_sentence == 'quit': break
            # 句子归一化
            input_sentence = normalizeString(input_sentence)
            # 生成响应Evaluate sentence
            output_words = evaluate(encoder, decoder, searcher, voc, input_sentence)
            # 去掉EOS后面的内容
            words = []
            for word in output_words:
                if word == 'EOS':
                    break
                elif word != 'PAD':
                    words.append(word)
            print('Bot:', ' '.join(words))

        except KeyError:
            print("Error: Encountered unknown word.")


# 配置模型
model_name = 'cb_model'
attn_model = 'dot'
# attn_model = 'general'
# attn_model = 'concat'
hidden_size = 500
encoder_n_layers = 2
decoder_n_layers = 2
dropout = 0.1
batch_size = 64

# 从哪个checkpoint恢复，如果是None，那么从头开始训练。
# loadFilename = None

loadFilename = "./model_Seq2seq/cb_model/cornell movie-dialogs corpus/2-2_500/5000_checkpoint.tar"
checkpoint_iter = 5000

# 如果loadFilename不空，则从中加载模型
if loadFilename:
    # 如果训练和加载是一条机器，那么直接加载
    checkpoint = torch.load(loadFilename)
    # 否则比如checkpoint是在GPU上得到的，但是我们现在又用CPU来训练或者测试，那么注释掉下面的代码
    # checkpoint = torch.load(loadFilename, map_location=torch.device('cpu'))
    encoder_sd = checkpoint['en']
    decoder_sd = checkpoint['de']
    encoder_optimizer_sd = checkpoint['en_opt']
    decoder_optimizer_sd = checkpoint['de_opt']
    embedding_sd = checkpoint['embedding']
    voc.__dict__ = checkpoint['voc_dict']

print('Building encoder and decoder ...')
# 初始化word embedding
embedding = nn.Embedding(voc.num_words, hidden_size)
if loadFilename:
    embedding.load_state_dict(embedding_sd)
# 初始化encoder和decoder模型
encoder = EncoderRNN(hidden_size, embedding, encoder_n_layers, dropout)
decoder = LuongAttnDecoderRNN(attn_model, embedding, hidden_size, voc.num_words,
                              decoder_n_layers, dropout)
if loadFilename:
    encoder.load_state_dict(encoder_sd)
    decoder.load_state_dict(decoder_sd)
# 使用合适的设备
encoder = encoder.to(device)
decoder = decoder.to(device)
print('Models built and ready to go!')


# 配置训练的超参数和优化器
clip = 50.0
teacher_forcing_ratio = 1.0
learning_rate = 0.0001
decoder_learning_ratio = 5.0
n_iteration = 5000
print_every = 1
save_every = 1000
save_dir = "./model_Seq2seq_1"


# 设置进入训练模式，从而开启dropout
encoder.train()
decoder.train()

# 初始化优化器
print('Building optimizers ...')
encoder_optimizer = optim.Adam(encoder.parameters(), lr=learning_rate)
decoder_optimizer = optim.Adam(decoder.parameters(), lr=learning_rate * decoder_learning_ratio)
if loadFilename:
    encoder_optimizer.load_state_dict(encoder_optimizer_sd)
    decoder_optimizer.load_state_dict(decoder_optimizer_sd)

# 开始训练
print("Starting Training!")
trainIters(model_name, voc, pairs, encoder, decoder, encoder_optimizer, decoder_optimizer,
           embedding, encoder_n_layers, decoder_n_layers, save_dir, n_iteration, batch_size,
           print_every, save_every, clip, corpus_name, loadFilename)

end_time = time.time()
print("time: %.1fs" % (end_time - start_time))


# 进入eval模式，从而去掉dropout。
encoder.eval()
decoder.eval()

# 构造searcher对象
searcher = GreedySearchDecoder(encoder, decoder)

# 测试
evaluateInput(encoder, decoder, searcher, voc)