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使用PyTorch构建多轮对话系统的示例代码。这个示例项目包括一个简单的Seq2Seq模型用于对话生成，并使用GRU作为RNN的变体。以下是代码的主要部分，包括数据预处理、模型定义和训练循环。

数据预处理

首先，准备数据并进行预处理。这部分代码假定你有一个对话数据集，格式为成对的问答句子。

import torch
import torch.nn as nn
import torch.optim as optim
from torch.utils.data import DataLoader, Dataset
import numpy as np
import random# 假设数据集是一个成对的问答列表
pairs = [["Hi, how are you?", "I'm good, thank you! How about you?"],["What is your name?", "My name is Chatbot."],# 添加更多对话数据
]# 简单的词汇表和索引映射
word2index = {"<PAD>": 0, "<SOS>": 1, "<EOS>": 2, "<UNK>": 3}
index2word = {0: "<PAD>", 1: "<SOS>", 2: "<EOS>", 3: "<UNK>"}
vocab_size = len(word2index)def tokenize(sentence):return sentence.lower().split()def build_vocab(pairs):global word2index, index2word, vocab_sizefor pair in pairs:for sentence in pair:for word in tokenize(sentence):if word not in word2index:word2index[word] = vocab_sizeindex2word[vocab_size] = wordvocab_size += 1def sentence_to_tensor(sentence):tokens = tokenize(sentence)indices = [word2index.get(word, word2index["<UNK>"]) for word in tokens]return torch.tensor(indices + [word2index["<EOS>"]], dtype=torch.long)build_vocab(pairs)

数据集和数据加载

定义一个Dataset类和DataLoader来加载数据。

class ChatDataset(Dataset):def __init__(self, pairs):self.pairs = pairsdef __len__(self):return len(self.pairs)def __getitem__(self, idx):input_tensor = sentence_to_tensor(self.pairs[idx][0])target_tensor = sentence_to_tensor(self.pairs[idx][1])return input_tensor, target_tensordef collate_fn(batch):inputs, targets = zip(*batch)input_lengths = [len(seq) for seq in inputs]target_lengths = [len(seq) for seq in targets]inputs = nn.utils.rnn.pad_sequence(inputs, padding_value=word2index["<PAD>"])targets = nn.utils.rnn.pad_sequence(targets, padding_value=word2index["<PAD>"])return inputs, targets, input_lengths, target_lengthsdataset = ChatDataset(pairs)
dataloader = DataLoader(dataset, batch_size=2, collate_fn=collate_fn, shuffle=True)

模型定义

定义一个简单的Seq2Seq模型，包括编码器和解码器。

class Encoder(nn.Module):def __init__(self, input_size, hidden_size, num_layers=1):super(Encoder, self).__init__()self.embedding = nn.Embedding(input_size, hidden_size)self.gru = nn.GRU(hidden_size, hidden_size, num_layers)def forward(self, input_seq, input_lengths, hidden=None):embedded = self.embedding(input_seq)packed = nn.utils.rnn.pack_padded_sequence(embedded, input_lengths, enforce_sorted=False)outputs, hidden = self.gru(packed, hidden)outputs, _ = nn.utils.rnn.pad_packed_sequence(outputs)return outputs, hiddenclass Decoder(nn.Module):def __init__(self, output_size, hidden_size, num_layers=1):super(Decoder, self).__init__()self.embedding = nn.Embedding(output_size, hidden_size)self.gru = nn.GRU(hidden_size, hidden_size, num_layers)self.out = nn.Linear(hidden_size, output_size)self.softmax = nn.LogSoftmax(dim=1)def forward(self, input_step, hidden, encoder_outputs):embedded = self.embedding(input_step)gru_output, hidden = self.gru(embedded, hidden)output = self.softmax(self.out(gru_output.squeeze(0)))return output, hiddenclass Seq2Seq(nn.Module):def __init__(self, encoder, decoder, device):super(Seq2Seq, self).__init__()self.encoder = encoderself.decoder = decoderself.device = devicedef forward(self, input_tensor, target_tensor, input_lengths, target_lengths, teacher_forcing_ratio=0.5):batch_size = input_tensor.size(1)max_target_len = max(target_lengths)vocab_size = self.decoder.out.out_featuresoutputs = torch.zeros(max_target_len, batch_size, vocab_size).to(self.device)encoder_outputs, encoder_hidden = self.encoder(input_tensor, input_lengths)decoder_input = torch.tensor([[word2index["<SOS>"]] * batch_size]).to(self.device)decoder_hidden = encoder_hiddenfor t in range(max_target_len):decoder_output, decoder_hidden = self.decoder(decoder_input, decoder_hidden, encoder_outputs)outputs[t] = decoder_outputtop1 = decoder_output.argmax(1)decoder_input = target_tensor[t].unsqueeze(0) if random.random() < teacher_forcing_ratio else top1.unsqueeze(0)return outputsdevice = torch.device("cuda" if torch.cuda.is_available() else "cpu")
encoder = Encoder(vocab_size, hidden_size=256).to(device)
decoder = Decoder(vocab_size, hidden_size=256).to(device)
model = Seq2Seq(encoder, decoder, device).to(device)

训练循环

定义训练循环并进行模型训练。

def train(model, dataloader, num_epochs, learning_rate=0.001):criterion = nn.CrossEntropyLoss(ignore_index=word2index["<PAD>"])optimizer = optim.Adam(model.parameters(), lr=learning_rate)for epoch in range(num_epochs):model.train()total_loss = 0for inputs, targets, input_lengths, target_lengths in dataloader:inputs, targets = inputs.to(device), targets.to(device)optimizer.zero_grad()outputs = model(inputs, targets, input_lengths, target_lengths)loss = criterion(outputs.view(-1, vocab_size), targets.view(-1))loss.backward()optimizer.step()total_loss += loss.item()print(f"Epoch [{epoch+1}/{num_epochs}], Loss: {total_loss/len(dataloader)}")train(model, dataloader, num_epochs=10)

测试与推理

定义一个简单的推理函数来进行对话生成。

def evaluate(model, sentence, max_length=10):model.eval()with torch.no_grad():input_tensor = sentence_to_tensor(sentence).unsqueeze(1).to(device)input_length = [input_tensor.size(0)]encoder_outputs, encoder_hidden = model.encoder(input_tensor, input_length)decoder_input = torch.tensor([[word2index["<SOS>"]]]).to(device)decoder_hidden = encoder_hiddendecoded_words = []for _ in range(max_length):decoder_output, decoder_hidden = model.decoder(decoder_input, decoder_hidden, encoder_outputs)top1 = decoder_output.argmax(1).item()if top1 == word2index["<EOS>"]:breakelse:decoded_words.append(index2word[top1])decoder_input = torch.tensor([[top1]]).to(device)return ' '.join(decoded_words)print(evaluate(model, "Hi, how are you?"))

总结

这只是一个简单的示例，用于展示如何使用PyTorch构建一个基本的多轮对话系统。实际应用中，可能需要更多的数据预处理、更复杂的模型（如Transformer）、更细致的训练策略和优化技术，以及更丰富的对话数据集。希望这个示例对你有所帮助！