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这是一个经典的文本分类问题，使用google的预训练模型BERT中文版bert-base-chinese来做中文文本分类。可以先在Huggingface上下载预训练模型备用。https://huggingface.co/google-bert/bert-base-chinese/tree/main

我使用的训练环境是

pip install torch==2.0.0;
pip install transformers==4.30.2;
pip install gensim==4.3.3;
pip install huggingface-hub==0.15.1;
pip install modelscope==1.20.1;

一、准备训练数据

1.1 准备中文文本分类任务的训练数据

这里Demo数据如下：

各银行信用卡挂失费迥异 北京银行收费最高    0
莫泰酒店流拍 大摩叫价或降至6亿美元 4
乌兹别克斯坦议会立法院主席获连任   6
德媒披露鲁能引援关键人物 是他力荐德甲亚洲强人    7
辉立证券给予广汽集团持有评级 2
图文-业余希望赛海南站第二轮 球场的菠萝蜜  7
陆毅鲍蕾：近乎完美的爱情(组图)(2)    9
7000亿美元救市方案将成期市毒药  0
保诚启动210亿美元配股交易以融资收购AIG部门   2

分类class类别文件：

finance
realty
stocks
education
science
society
politics
sports
game
entertainment

1.2 数据读取和截断，使满足BERT模型输入

读取训练数据，对文本进行处理，如截取过长的文本、补齐较短的文本，加上起始标示、对文本进行编码、添加掩码、转为tensor等操作。

import os
from config import parsers
from transformers import BertTokenizer
from torch.utils.data import Dataset, DataLoader
import torchfrom transformers import AutoTokenizer, AutoModelForMaskedLMdef read_data(file):# 读取文件all_data = open(file, "r", encoding="utf-8").read().split("\n")# 得到所有文本、所有标签、句子的最大长度texts, labels, max_length = [], [], []for data in all_data:if data:text, label = data.split("\t")max_length.append(len(text))texts.append(text)labels.append(label)# 根据不同的数据集返回不同的内容if os.path.split(file)[1] == "train.txt":max_len = max(max_length)return texts, labels, max_lenreturn texts, labels,class MyDataset(Dataset):def __init__(self, texts, labels, max_length):self.all_text = textsself.all_label = labelsself.max_len = max_lengthself.tokenizer = BertTokenizer.from_pretrained(parsers().bert_pred)
#         self.tokenizer = AutoTokenizer.from_pretrained("bert-base-chinese")def __getitem__(self, index):# 取出一条数据并截断长度text = self.all_text[index][:self.max_len]label = self.all_label[index]# 分词text_id = self.tokenizer.tokenize(text)# 加上起始标志text_id = ["[CLS]"] + text_id# 编码token_id = self.tokenizer.convert_tokens_to_ids(text_id)# 掩码  -》mask = [1] * len(token_id) + [0] * (self.max_len + 2 - len(token_id))# 编码后  -》长度一致token_ids = token_id + [0] * (self.max_len + 2 - len(token_id))# str -》 intlabel = int(label)# 转化成tensortoken_ids = torch.tensor(token_ids)mask = torch.tensor(mask)label = torch.tensor(label)return (token_ids, mask), labeldef __len__(self):# 得到文本的长度return len(self.all_text)

将文本处理后，就可以使用torch.utils.data中自带的DataLoader模块来加载训练数据了。

二、微调BERT模型

我们是微调BERT模型，需要获取BERT最后一个隐藏层的输出作为输入到下一个全连接层。

至于选择BERT模型的哪个输出作为linear层的输入，可以通过实验尝试，或者遵循常理。

pooler_output：这是通过将最后一层的隐藏状态的第一个token（通常是[CLS] token）通过一个线性层和激活函数得到的输出，常用于分类任务。
last_hidden_state：这是模型所有层的最后一个隐藏状态的输出，包含了整个序列的上下文信息，适用于序列级别的任务。

简单调用下BERT模型，打印出来最后一层看下：

import torch
import time
import torch.nn as nn
from transformers import BertTokenizer
from transformers import BertModel
from transformers import AutoTokenizer, AutoModelForMaskedLMdef process_text(text, bert_pred):tokenizer = BertTokenizer.from_pretrained(bert_pred)token_id = tokenizer.convert_tokens_to_ids(["[CLS]"] + tokenizer.tokenize(text))mask = [1] * len(token_id) + [0] * (38 + 2 - len(token_id))token_ids = token_id + [0] * (38 + 2 - len(token_id))token_ids = torch.tensor(token_ids).unsqueeze(0)mask = torch.tensor(mask).unsqueeze(0)x = torch.stack([token_ids, mask])return xdevice = "cpu"
bert = BertModel.from_pretrained('./bert-base-chinese/')
texts = ["沈腾和马丽的电影《独行月球》挺好看"]
for text in texts:x = process_text(text, './bert-base-chinese/')input_ids, attention_mask = x[0].to(device), x[1].to(device)hidden_out = bert(input_ids, attention_mask=attention_mask,output_hidden_states=False) print(hidden_out)

 输出结果：

2.1 文本分类任务，选择使用pooler_output作为线性层的输入。

import torch.nn as nn
from transformers import BertModel
from transformers import AutoTokenizer, AutoModelForMaskedLM
from config import parsers
import torchclass MyModel(nn.Module):def __init__(self):super(MyModel, self).__init__()self.args = parsers()self.device = "cuda:0" if torch.cuda.is_available() else "cpu"  self.bert = BertModel.from_pretrained(self.args.bert_pred) # bert 模型进行微调for param in self.bert.parameters():param.requires_grad = True# 一个全连接层self.linear = nn.Linear(self.args.num_filters, self.args.class_num)def forward(self, x):input_ids, attention_mask = x[0].to(self.device), x[1].to(self.device)hidden_out = self.bert(input_ids, attention_mask=attention_mask,output_hidden_states=False)  # 是否输出所有encoder层的结果# shape (batch_size, hidden_size)  pooler_output -->  hidden_out[0]pred = self.linear(hidden_out.pooler_output)# 返回预测结果return pred

2.2 优化器使用Adam、损失函数使用交叉熵损失函数

device = "cuda:0" if torch.cuda.is_available() else "cpu"
model = MyModel().to(device)
opt = AdamW(model.parameters(), lr=args.learn_rate)
loss_fn = nn.CrossEntropyLoss()

三、训练模型

3.1 参数配置

def parsers():parser = argparse.ArgumentParser(description="Bert model of argparse")parser.add_argument("tx_date",nargs='?') #可选输入参数，计算日期parser.add_argument("--train_file", type=str, default=os.path.join("./data_all", "train.txt"))parser.add_argument("--dev_file", type=str, default=os.path.join("./data_all", "dev.txt"))parser.add_argument("--test_file", type=str, default=os.path.join("./data_all", "test.txt"))parser.add_argument("--classification", type=str, default=os.path.join("./data_all", "class.txt"))parser.add_argument("--bert_pred", type=str, default="./bert-base-chinese")parser.add_argument("--class_num", type=int, default=12)parser.add_argument("--max_len", type=int, default=38)parser.add_argument("--batch_size", type=int, default=32)parser.add_argument("--epochs", type=int, default=10)parser.add_argument("--learn_rate", type=float, default=1e-5)parser.add_argument("--num_filters", type=int, default=768)parser.add_argument("--save_model_best", type=str, default=os.path.join("model", "all_best_model.pth"))parser.add_argument("--save_model_last", type=str, default=os.path.join("model", "all_last_model.pth"))args = parser.parse_args()return args

3.2 模型训练

import torch
from torch.utils.data import DataLoader
from torch.optim import AdamW
import torch.nn as nn
from sklearn.metrics import accuracy_score
import timeif __name__ == "__main__":start = time.time()args = parsers()device = "cuda:0" if torch.cuda.is_available() else "cpu"print("device:", device)train_text, train_label, max_len = read_data(args.train_file)dev_text, dev_label = read_data(args.dev_file)args.max_len = max_lentrain_dataset = MyDataset(train_text, train_label, args.max_len)train_dataloader = DataLoader(train_dataset, batch_size=args.batch_size, shuffle=True)dev_dataset = MyDataset(dev_text, dev_label, args.max_len)dev_dataloader = DataLoader(dev_dataset, batch_size=args.batch_size, shuffle=False)model = MyModel().to(device)opt = AdamW(model.parameters(), lr=args.learn_rate)loss_fn = nn.CrossEntropyLoss()acc_max = float("-inf")for epoch in range(args.epochs):loss_sum, count = 0, 0model.train()for batch_index, (batch_text, batch_label) in enumerate(train_dataloader):batch_label = batch_label.to(device)pred = model(batch_text)loss = loss_fn(pred, batch_label)opt.zero_grad()loss.backward()opt.step()loss_sum += losscount += 1# 打印内容if len(train_dataloader) - batch_index <= len(train_dataloader) % 1000 and count == len(train_dataloader) % 1000:msg = "[{0}/{1:5d}]\tTrain_Loss:{2:.4f}"print(msg.format(epoch + 1, batch_index + 1, loss_sum / count))loss_sum, count = 0.0, 0if batch_index % 1000 == 999:msg = "[{0}/{1:5d}]\tTrain_Loss:{2:.4f}"print(msg.format(epoch + 1, batch_index + 1, loss_sum / count))loss_sum, count = 0.0, 0model.eval()all_pred, all_true = [], []with torch.no_grad():for batch_text, batch_label in dev_dataloader:batch_label = batch_label.to(device)pred = model(batch_text)pred = torch.argmax(pred, dim=1).cpu().numpy().tolist()label = batch_label.cpu().numpy().tolist()all_pred.extend(pred)all_true.extend(label)acc = accuracy_score(all_pred, all_true)print(f"dev acc:{acc:.4f}")if acc > acc_max:print(acc, acc_max)acc_max = acctorch.save(model.state_dict(), args.save_model_best)print(f"以保存最佳模型")torch.save(model.state_dict(), args.save_model_last)end = time.time()print(f"运行时间：{(end-start)/60%60:.4f} min")

模型保存为：

-rw-rw-r--  1 gaoToby gaoToby 391M Dec 24 14:02 all_best_model.pth
-rw-rw-r--  1 gaoToby gaoToby 391M Dec 24 14:02 all_last_model.pth

四、模型推理预测

准备预测文本文件，加载模型，进行文本的类别预测。

def text_class_name(pred):result = torch.argmax(pred, dim=1)print(torch.argmax(pred, dim=1).cpu().numpy().tolist())result = result.cpu().numpy().tolist()classification = open(args.classification, "r", encoding="utf-8").read().split("\n")classification_dict = dict(zip(range(len(classification)), classification))print(f"文本：{text}\t预测的类别为：{classification_dict[result[0]]}")if __name__ == "__main__":start = time.time()args = parsers()device = "cuda:0" if torch.cuda.is_available() else "cpu"model = load_model(device, args.save_model_best)texts = ["沈腾和马丽的新电影《独行月球》好看", "最近金融环境不太好，投资需谨慎"]print("模型预测结果：")for text in texts:x = process_text(text, args.bert_pred)with torch.no_grad():pred = model(x)text_class_name(pred)end = time.time()print(f"耗时为：{end - start} s")

以上，基本流程完成。当然模型还需要调优来改进预测效果的。

代码是实际跑通的，我训练和预测均使用的是GPU。如果是使用GPU做模型训练，再使用CPU做推理预测的情况，推理预测加载模型的时候注意修改下：

 myModel.load_state_dict(torch.load(model_path, map_location=torch.device('cpu')))

Done