!pip install git+https://github.com/d2l-ai/d2l-zh@release # installing d2l import collections import math import torch from torch import nn from d2l import torch as d2l #@save class Seq2SeqEncoder(d2l.Encoder): """用于序列到序列学习的循环神经网络编码器""" def __init__(self, vocab_size, embed_size, num_hiddens, num_layers, dropout=0, **kwargs): super(Seq2SeqEncoder, self).__init__(**kwargs) # 嵌入层 self.embedding = nn.Embedding(vocab_size, embed_size) self.rnn = nn.GRU(embed_size, num_hiddens, num_layers, dropout=dropout) def forward(self, X, *args): # 输出'X'的形状：(batch_size,num_steps,embed_size) X = self.embedding(X) # 在循环神经网络模型中，第一个轴对应于时间步 X = X.permute(1, 0, 2) # 如果未提及状态，则默认为0 output, state = self.rnn(X) # output的形状:(num_steps,batch_size,num_hiddens) # state的形状:(num_layers,batch_size,num_hiddens) return output, state encoder = Seq2SeqEncoder(vocab_size=10, embed_size=8, num_hiddens=16, num_layers=2) encoder.eval() X = torch.zeros((4, 7), dtype=torch.long) output, state = encoder(X) output.shape state.shape class Seq2SeqDecoder(d2l.Decoder): """用于序列到序列学习的循环神经网络解码器""" def __init__(self, vocab_size, embed_size, num_hiddens, num_layers, dropout=0, **kwargs): super(Seq2SeqDecoder, self).__init__(**kwargs) self.embedding = nn.Embedding(vocab_size, embed_size) self.rnn = nn.GRU(embed_size + num_hiddens, num_hiddens, num_layers, dropout=dropout) self.dense = nn.Linear(num_hiddens, vocab_size) def init_state(self, enc_outputs, *args): return enc_outputs[1] def forward(self, X, state): # 输出'X'的形状：(batch_size,num_steps,embed_size) X = self.embedding(X).permute(1, 0, 2) # 广播context，使其具有与X相同的num_steps context = state[-1].repeat(X.shape[0], 1, 1) X_and_context = torch.cat((X, context), 2) output, state = self.rnn(X_and_context, state) output = self.dense(output).permute(1, 0, 2) # output的形状:(batch_size,num_steps,vocab_size) # state的形状:(num_layers,batch_size,num_hiddens) return output, state decoder = Seq2SeqDecoder(vocab_size=10, embed_size=8, num_hiddens=16, num_layers=2) decoder.eval() state = decoder.init_state(encoder(X)) output, state = decoder(X, state) output.shape, state.shape #@save def sequence_mask(X, valid_len, value=0): """在序列中屏蔽不相关的项""" maxlen = X.size(1) mask = torch.arange((maxlen), dtype=torch.float32, device=X.device)[None, :] < valid_len[:, None] X[~mask] = value return X X = torch.tensor([[1, 2, 3], [4, 5, 6]]) sequence_mask(X, torch.tensor([1, 2])) X = torch.ones(2, 3, 4) sequence_mask(X, torch.tensor([1, 2]), value=-1) #@save class MaskedSoftmaxCELoss(nn.CrossEntropyLoss): """带遮蔽的softmax交叉熵损失函数""" # pred的形状：(batch_size,num_steps,vocab_size) # label的形状：(batch_size,num_steps) # valid_len的形状：(batch_size,) def forward(self, pred, label, valid_len): weights = torch.ones_like(label) weights = sequence_mask(weights, valid_len) self.reduction='none' unweighted_loss = super(MaskedSoftmaxCELoss, self).forward( pred.permute(0, 2, 1), label) weighted_loss = (unweighted_loss * weights).mean(dim=1) return weighted_loss loss = MaskedSoftmaxCELoss() loss(torch.ones(3, 4, 10), torch.ones((3, 4), dtype=torch.long), torch.tensor([4, 2, 0])) #@save def train_seq2seq(net, data_iter, lr, num_epochs, tgt_vocab, device): """训练序列到序列模型""" def xavier_init_weights(m): if type(m) == nn.Linear: nn.init.xavier_uniform_(m.weight) if type(m) == nn.GRU: for param in m._flat_weights_names: if "weight" in param: nn.init.xavier_uniform_(m._parameters[param]) net.apply(xavier_init_weights) net.to(device) optimizer = torch.optim.Adam(net.parameters(), lr=lr) loss = MaskedSoftmaxCELoss() net.train() animator = d2l.Animator(xlabel='epoch', ylabel='loss', xlim=[10, num_epochs]) for epoch in range(num_epochs): timer = d2l.Timer() metric = d2l.Accumulator(2) # 训练损失总和，词元数量 for batch in data_iter: optimizer.zero_grad() X, X_valid_len, Y, Y_valid_len = [x.to(device) for x in batch] bos = torch.tensor([tgt_vocab['']] * Y.shape[0], device=device).reshape(-1, 1) dec_input = torch.cat([bos, Y[:, :-1]], 1) # 强制教学 Y_hat, _ = net(X, dec_input, X_valid_len) l = loss(Y_hat, Y, Y_valid_len) l.sum().backward() # 损失函数的标量进行“反向传播” d2l.grad_clipping(net, 1) num_tokens = Y_valid_len.sum() optimizer.step() with torch.no_grad(): metric.add(l.sum(), num_tokens) if (epoch + 1) % 10 == 0: animator.add(epoch + 1, (metric[0] / metric[1],)) print(f'loss {metric[0] / metric[1]:.3f}, {metric[1] / timer.stop():.1f} ' f'tokens/sec on {str(device)}') embed_size, num_hiddens, num_layers, dropout = 32, 32, 2, 0.1 batch_size, num_steps = 64, 10 lr, num_epochs, device = 0.005, 300, d2l.try_gpu() train_iter, src_vocab, tgt_vocab = d2l.load_data_nmt(batch_size, num_steps) encoder = Seq2SeqEncoder(len(src_vocab), embed_size, num_hiddens, num_layers, dropout) decoder = Seq2SeqDecoder(len(tgt_vocab), embed_size, num_hiddens, num_layers, dropout) net = d2l.EncoderDecoder(encoder, decoder) train_seq2seq(net, train_iter, lr, num_epochs, tgt_vocab, device) #@save def predict_seq2seq(net, src_sentence, src_vocab, tgt_vocab, num_steps, device, save_attention_weights=False): """序列到序列模型的预测""" # 在预测时将net设置为评估模式 net.eval() src_tokens = src_vocab[src_sentence.lower().split(' ')] + [ src_vocab['']] enc_valid_len = torch.tensor([len(src_tokens)], device=device) src_tokens = d2l.truncate_pad(src_tokens, num_steps, src_vocab['']) # 添加批量轴 enc_X = torch.unsqueeze( torch.tensor(src_tokens, dtype=torch.long, device=device), dim=0) enc_outputs = net.encoder(enc_X, enc_valid_len) dec_state = net.decoder.init_state(enc_outputs, enc_valid_len) # 添加批量轴 dec_X = torch.unsqueeze(torch.tensor( [tgt_vocab['']], dtype=torch.long, device=device), dim=0) output_seq, attention_weight_seq = [], [] for _ in range(num_steps): Y, dec_state = net.decoder(dec_X, dec_state) # 我们使用具有预测最高可能性的词元，作为解码器在下一时间步的输入 dec_X = Y.argmax(dim=2) pred = dec_X.squeeze(dim=0).type(torch.int32).item() # 保存注意力权重（稍后讨论） if save_attention_weights: attention_weight_seq.append(net.decoder.attention_weights) # 一旦序列结束词元被预测，输出序列的生成就完成了 if pred == tgt_vocab['']: break output_seq.append(pred) return ' '.join(tgt_vocab.to_tokens(output_seq)), attention_weight_seq def bleu(pred_seq, label_seq, k): #@save """计算BLEU""" pred_tokens, label_tokens = pred_seq.split(' '), label_seq.split(' ') len_pred, len_label = len(pred_tokens), len(label_tokens) score = math.exp(min(0, 1 - len_label / len_pred)) for n in range(1, k + 1): num_matches, label_subs = 0, collections.defaultdict(int) for i in range(len_label - n + 1): label_subs[' '.join(label_tokens[i: i + n])] += 1 for i in range(len_pred - n + 1): if label_subs[' '.join(pred_tokens[i: i + n])] > 0: num_matches += 1 label_subs[' '.join(pred_tokens[i: i + n])] -= 1 score *= math.pow(num_matches / (len_pred - n + 1), math.pow(0.5, n)) return score engs = ['go .', "i lost .", 'he\'s calm .', 'i\'m home .'] fras = ['va !', 'j\'ai perdu .', 'il est calme .', 'je suis chez moi .'] for eng, fra in zip(engs, fras): translation, attention_weight_seq = predict_seq2seq( net, eng, src_vocab, tgt_vocab, num_steps, device) print(f'{eng} => {translation}, bleu {bleu(translation, fra, k=2):.3f}')