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PyTorch环境下对BERT进行Fine-tuning

發布時間：2025/3/21 编程问答 47 豆豆

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PyTorch環境下對BERT進行Fine-tuning

本文根據Chris McCormick的BERT微調教程進行優化并使其適應于數據集Quora Question Pairs里的判斷問題對是否一致的任務。（文字部分大部分為原文的翻譯）

原文博客地址：https://mccormickml.com/2019/07/22/BERT-fine-tuning/

原文colab地址：https://colab.research.google.com/drive/1pTuQhug6Dhl9XalKB0zUGf4FIdYFlpcX

本文項目地址：https://github.com/yxf975/pretraining_models_learning

前言

本文對刪除了很多原英文博文中一些介紹性的內容，著重于如何實現基礎的BERT微調方法。本解決方法不同于Chris McCormick的有以下幾點：

使用的數據集為Quora問題對數據集
添加了多gpu運行的選擇
將部分代碼封裝進了函數中，方便使用
添加了預測部分

具體對于BERT等預訓練模型的原理的理解，我會單獨創建一個話題，讓我們直接開始吧！

準備工作

檢查GPU

為了讓 torch 使用 GPU，我們需要識別并指定 GPU 作為設備。稍后，在我們的訓練循環中，我們將把數據加載到設備上。

import torch# If there's a GPU available... if torch.cuda.is_available(): # Tell PyTorch to use the GPU. device = torch.device("cuda")n_gpu = torch.cuda.device_count()print('There are %d GPU(s) available.' % n_gpu)print('We will use the GPU:', [torch.cuda.get_device_name(i) for i in range(n_gpu)])# If not... else:print('No GPU available, using the CPU instead.')device = torch.device("cpu")

安裝Transformer庫

目前，Hugging Face的Transformer庫似乎是最被廣泛接受的、最強大的與BERT合作的pytorch接口。除了支持各種不同的預先訓練好的變換模型外，該庫還包含了這些模型的預構建修改，適合你的特定任務。例如，在本教程中，我們將使用BertForSequenceClassification。

該庫還包括用于標記分類、問題回答、下句預測等的特定任務類。使用這些預建的類可以簡化為您的目的修改BERT的過程。

！pip install transformers

加載Quora Question Pairs數據

數據集在kaggle官網上，注冊登錄即可下載，下載地址：https://www.kaggle.com/c/quora-question-pairs 。另外本人在google drive上也共享了數據集，下載地址：https://drive.google.com/drive/folders/1kFkte0Kt2xLe6Ykl4O4_TrL2iCzorOYk

Quora Question Pairs數據集介紹

這個數據集針對于Quora平臺，很多人在Quora上會提出類似措辭的問題。具有相同意圖的多個問題可能會導致搜尋者花費更多時間來尋找問題的最佳答案，并使作者感到他們需要回答同一問題的多個版本。

該任務需要對問題對是否重復進行分類，從而解決自然語言處理問題。這樣做將使查找問題的高質量答案變得更加容易，從而為Quora的作家，搜尋者和讀者帶來了更好的體驗。

pandas加載數據

import pandas as pd import numpy as np# Load the dataset into a pandas dataframe. train_data = pd.read_csv("./train.csv", index_col="id",nrows=10000) train_data.head(6)

這里我顯示6行，因為到第六行才有個正樣本。

idqid1qid2question1question2is_duplicate

0	1	2	What is the step by step guide to invest in share market in india?	What is the step by step guide to invest in share market?	0
1	3	4	What is the story of Kohinoor (Koh-i-Noor) Diamond?	What would happen if the Indian government stole the Kohinoor (Koh-i-Noor) diamond back?	0
2	5	6	How can I increase the speed of my internet connection while using a VPN?	How can Internet speed be increased by hacking through DNS?	0
3	7	8	Why am I mentally very lonely? How can I solve it?	Find the remainder when [math]23^{24}[/math] is divided by 24,23?	0
4	9	10	Which one dissolve in water quikly sugar, salt, methane and carbon di oxide?	Which fish would survive in salt water?	0
5	11	12	Astrology: I am a Capricorn Sun Cap moon and cap rising…what does that say about me?	I’m a triple Capricorn (Sun, Moon and ascendant in Capricorn) What does this say about me?	1

我們實際關心的三個屬性是"question1"，“question1"和它們的標簽"is_duplicate”，這個標簽被稱為"是否重復"（0=不重復，1=重復）。

訓練集驗證集拆分

把我們的訓練集分成 80% 用于訓練，20% 用于驗證。

from sklearn.model_selection import train_test_split# train_validation data split X_train, X_val, y_train, y_val = train_test_split(train_data[["question1", "question2"]], train_data["is_duplicate"], test_size=0.2, random_state=405633)

Tokenization & Input 格式化

BERT Tokenizer

from transformers import BertTokenizer# load bert tokenizer tokenizer = BertTokenizer.from_pretrained('bert-base-uncased', do_lower_case=True)

查看數據中句子的最長長度

#calculate the maximum sentence length max_len = 0 for _, row in train_data.iterrows():max_len = max(max_len, len(tokenizer(row['question1'],row['question2'])["input_ids"]))print("max token length of the input:", max_len)# set the maximum token length max_length = pow(2,int(np.log2(max_len)+1)) print("max token length for BERT:", max_length)

轉換為BERT輸入

from torch.utils.data import TensorDataset# func to convert data to bert input def convert_to_dataset_torch(data: pd.DataFrame, labels = pd.Series(data=None)) -> TensorDataset:input_ids = []attention_masks = []token_type_ids = []for _, row in tqdm(data.iterrows(), total=data.shape[0]):encoded_dict = tokenizer.encode_plus(row["question1"], row["question2"], max_length=max_length, pad_to_max_length=True, return_attention_mask=True, return_tensors='pt', truncation=True)# Add the encoded sentences to the list.input_ids.append(encoded_dict['input_ids'])token_type_ids.append(encoded_dict["token_type_ids"])# And its attention mask (simply differentiates padding from non-padding).attention_masks.append(encoded_dict['attention_mask'])# Convert the lists into tensors.input_ids = torch.cat(input_ids, dim=0)token_type_ids = torch.cat(token_type_ids, dim=0)attention_masks = torch.cat(attention_masks, dim=0)if labels.empty:return TensorDataset(input_ids, attention_masks, token_type_ids)else:labels = torch.tensor(labels.values)return TensorDataset(input_ids, attention_masks, token_type_ids, labels)

train = convert_to_dataset_torch(X_train, y_train) validation = convert_to_dataset_torch(X_val, y_val)

將數據放入DataLoader

我們還將使用 torch DataLoader 類為我們的數據集創建一個迭代器。這有助于在訓練過程中節省內存，因為與for循環不同，有了迭代器，整個數據集不需要加載到內存中。

from torch.utils.data import DataLoader, RandomSampler, SequentialSampler# set batch size for DataLoader(options from paper:16 or 32) batch_size = 32# Create the DataLoaders for training and validation sets train_dataloader = DataLoader(train, sampler = RandomSampler(train), # Select batches randomlybatch_size = batch_size )# For validation validation_dataloader = DataLoader(validation, sampler = SequentialSampler(validation), # Pull out batches sequentially.batch_size = batch_size )

加載模型

加載預訓練模型BertForSequenceClassification

我們將使用BertForSequenceClassification。這是普通的BERT模型，上面增加了一個用于分類的單線性層，我們將使用它作為句子分類器。當我們輸入數據時，整個預先訓練好的BERT模型和額外的未經訓練的分類層會根據我們的特定任務進行訓練。

from transformers import BertForSequenceClassification, AdamW, BertConfig# Load BertForSequenceClassification, the pretrained BERT model with a single # linear classification layer on top. model = BertForSequenceClassification.from_pretrained("bert-base-uncased", # Use the 12-layer BERT model, with an uncased vocab.num_labels = 2, # The number of output labels--2 for binary classification.# You can increase this for multi-class tasks. output_attentions = False, # Whether the model returns attentions weights.output_hidden_states = False, # Whether the model returns all hidden-states. )# Tell pytorch to run this model on the GPU. model.cuda() if n_gpu > 1:model = torch.nn.DataParallel(model)

當然也可以對BERT網絡結構進行修改以適應我們的任務，這里我就直接使用原模型。

優化器 & 學習率調度器

為了微調的目的，BERT論文的作者建議從以下數值中選擇（來自BERT論文的附錄A.3）。

batch大小：?16，32。（在Dataloader里設置）
學習率(Adam)：?5e-5、3e-5、2e-5。
epoch數：?2、3、4。

from transformers import get_linear_schedule_with_warmupoptimizer = AdamW(model.parameters(),lr = 2e-5, # args.learning_rateeps = 1e-8 # args.adam_epsilon)# Number of training epochs epochs = 2# Total number of training steps is [number of batches] x [number of epochs]. total_steps = len(train_dataloader) * epochs# Create the learning rate scheduler. scheduler = get_linear_schedule_with_warmup(optimizer, num_warmup_steps = 0, # Default value in run_glue.pynum_training_steps = total_steps)

訓練

時間規范函數

import time import datetime# Helper function for formatting elapsed times as hh:mm:ss def format_time(elapsed):'''Takes a time in seconds and returns a string hh:mm:ss'''# Round to the nearest second.elapsed_rounded = int(round((elapsed)))# Format as hh:mm:ssreturn str(datetime.timedelta(seconds=elapsed_rounded))

fit函數

from tqdm import tqdmdef fit_batch(dataloader, model, optimizer, epoch):total_train_loss = 0for batch in tqdm(dataloader, desc=f"Training epoch:{epoch+1}", unit="batch"):# Unpack batch from dataloader.input_ids = batch[0].to(device)attention_masks = batch[1].to(device)token_type_ids = batch[2].to(device)labels = batch[3].to(device)# clear any previously calculated gradients before performing a backward pass.model.zero_grad()# Perform a forward pass (evaluate the model on this training batch).outputs = model(input_ids, token_type_ids=token_type_ids, attention_mask=attention_masks, labels=labels)loss = outputs[0]total_train_loss += loss.item()# Perform a backward pass to calculate the gradients.loss.backward()# normlization of the gradients to 1.0 to avoid exploding gradientstorch.nn.utils.clip_grad_norm_(model.parameters(), 1.0)# Update parameters and take a step using the computed gradient.optimizer.step()# Update the learning rate.scheduler.step()return total_train_loss

驗證評估函數

from sklearn.metrics import accuracy_scoredef eval_batch(dataloader, model, metric=accuracy_score):total_eval_accuracy = 0total_eval_loss = 0predictions , predicted_labels = [], []for batch in tqdm(dataloader, desc="Evaluating", unit="batch"):# Unpack batch from dataloader.input_ids = batch[0].to(device)attention_masks = batch[1].to(device)token_type_ids = batch[2].to(device)labels = batch[3].to(device)# Tell pytorch not to bother with constructing the compute graph during# the forward pass, since this is only needed for backprop (training).with torch.no_grad():# Forward pass, calculate logit predictions.outputs = model(input_ids, token_type_ids=token_type_ids, attention_mask=attention_masks,labels=labels)loss = outputs[0]logits = outputs[1]total_eval_loss += loss.item()# Move logits and labels to CPUlogits = logits.detach().cpu().numpy()label_ids = labels.to('cpu').numpy()# Calculate the accuracy for this batch of validation sentences, and# accumulate it over all batches.y_pred = np.argmax(logits, axis=1).flatten()total_eval_accuracy += metric(label_ids, y_pred)predictions.extend(logits.tolist())predicted_labels.extend(y_pred.tolist())return total_eval_accuracy, total_eval_loss, predictions ,predicted_labels

訓練函數

def train(train_dataloader, validation_dataloader, model, optimizer, epochs):# list to store a number of quantities such as # training and validation loss, validation accuracy, and timings.training_stats = []# Measure the total training time for the whole run.total_t0 = time.time()for epoch in range(0, epochs):# Measure how long the training epoch takes.t0 = time.time()# Reset the total loss for this epoch.total_train_loss = 0# Put the model into training mode. model.train()total_train_loss = fit_batch(train_dataloader, model, optimizer, epoch)# Calculate the average loss over all of the batches.avg_train_loss = total_train_loss / len(train_dataloader)# Measure how long this epoch took.training_time = format_time(time.time() - t0)t0 = time.time()# Put the model in evaluation mode--the dropout layers behave differently# during evaluation.model.eval()total_eval_accuracy, total_eval_loss, _, _ = eval_batch(validation_dataloader, model)# Report the final accuracy for this validation run.avg_val_accuracy = total_eval_accuracy / len(validation_dataloader)print("\n")print(f"score: {avg_val_accuracy}")# Calculate the average loss over all of the batches.avg_val_loss = total_eval_loss / len(validation_dataloader)# Measure how long the validation run took.validation_time = format_time(time.time() - t0)print(f"Validation Loss: {avg_val_loss}")print("\n")# Record all statistics from this epoch.training_stats.append({'epoch': epoch,'Training Loss': avg_train_loss,'Valid. Loss': avg_val_loss,'Valid. score.': avg_val_accuracy,'Training Time': training_time,'Validation Time': validation_time})print("")print("Training complete!")print(f"Total training took {format_time(time.time()-total_t0)}")return training_stats

開始訓練

import random# Set the seed value all over the place to make this reproducible. seed_val = 2020random.seed(seed_val) np.random.seed(seed_val) torch.manual_seed(seed_val) if n_gpu > 0:torch.cuda.manual_seed_all(seed_val)training_stats = train(train_dataloader, validation_dataloader, model, optimizer, epochs)

查看訓練過程中的的評估數據

df_stats = pd.DataFrame(training_stats).set_index('epoch') df_stats

預測

預測函數

def predict(dataloader, model):prediction = list()for batch in tqdm(dataloader, desc="predicting", unit="batch"):# Unpack batch from dataloader.input_ids = batch[0].to(device)attention_masks = batch[1].to(device)token_type_ids = batch[2].to(device)# Tell pytorch not to bother with constructing the compute graph during# the forward pass, since this is only needed for backprop (training).with torch.no_grad():# Forward pass, calculate logit predictions.outputs = model(input_ids, token_type_ids=token_type_ids, attention_mask=attention_masks)logits = outputs[0]# Move logits and labels to CPUlogits = logits.detach().cpu().numpy()prediction.append(logits)pred_logits = np.concatenate(prediction, axis=0)pred_label = np.argmax(pred_logits, axis=1).flatten()print("done")return (pred_label,pred_logits)

為測試集創建Dataloader

# Create the DataLoader for test data. prediction_data = convert_to_dataset_torch(test_data) prediction_sampler = SequentialSampler(prediction_data) prediction_dataloader = DataLoader(prediction_data, sampler=prediction_sampler, batch_size=batch_size)

預測

也可以用softmax將logits轉化為相應的概率

y_pred,logits = predict(prediction_dataloader,model) # get the corresponding probablities prob = torch.nn.functional.softmax(torch.tensor(logits))

總結

本篇文章演示了利用預先訓練好的 BERT 模型，微調適應于Quora問題對任務。在面對其他類似的文本分類問題時也可以采取類似的微調方法。

當然如果想要更精確的更好的預測結果，可能需要使用更好的更合適的預訓練模型，修改網絡模型使之更適合當前任務，或者加入對抗訓練等方法。

總結

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