李宏毅-hw7-利用Bert完成QA

一、查漏补缺、熟能生巧：

        只有熬过不熟练的时期，反复琢磨，才会有熟练之后，藐视众生的时刻

1.关于transformers中的tokenizer的用法的简单介绍：

from transformers import BertTokenizerFast

# 加载预训练的BERT模型tokenizer
tokenizer = BertTokenizerFast.from_pretrained('bert-base-uncased')

# 文本输入
text = "This is an example sentence."

# 对文本进行分词和标记化
tokens = tokenizer(text, truncation=True, padding=True)

# 获取分词后的token IDs
input_ids = tokens['input_ids']

# 获取token类型IDs
token_type_ids = tokens['token_type_ids']

# 获取注意力遮罩
attention_mask = tokens['attention_mask']

print("Token IDs:", input_ids)
print("Token Type IDs:", token_type_ids)
print("Attention Mask:", attention_mask)

运行结果如下：

Token IDs: [101, 2023, 2003, 2019, 2742, 6251, 102]

Token Type IDs: [0, 0, 0, 0, 0, 0, 0]

Attention Mask: [1, 1, 1, 1, 1, 1, 1]

2.char_to_token的用法和作用说明：

from transformers import BertTokenizer

# 初始化BERT分词器
tokenizer = BertTokenizer.from_pretrained('bert-base-chinese')

# 原始文本
text = "我爱自然语言处理"

# 分词
tokens = tokenizer.tokenize(text)
print("分词后的标记序列:", tokens)

# 字符级别的索引
char_index = 3

# 将标记序列转换为句子字符串，并查找字符在句子字符串中的位置
sentence = tokenizer.convert_tokens_to_string(tokens)
char_position = sentence.index(text[char_index])
print("字符级别索引 {} 对应的句子字符串位置为: {}".format(char_index, char_position))

# 将标记序列转换为ID序列
input_ids = tokenizer.convert_tokens_to_ids(tokens)
print("ID序列:", input_ids)

输出结果：

分词后的标记序列: ['我', '爱', '自', '然', '语', '言', '处', '理']
字符级别索引 3 对应的句子字符串位置为: 6
ID序列: [2769, 4263, 5632, 4197, 6427, 6241, 1905, 4415]

上面的红色字体说明得不准确，下面是准确的“分词”的描述

3.关于list中：max_len允许本来的长度不够，那就返回本来长度的数值:

tokenized_question.ids[:self.max_question_len]

#测试：
test = [1,2,3,4]
print(test[:100])

输出：[1, 2, 3, 4]

4.

二、代码研读：

version_1:助教版本的代码：

#下载data数据
# Download link 1
!gdown --id '1AVgZvy3VFeg0fX-6WQJMHPVrx3A-M1kb' --output hw7_data.zip

# Download Link 2 (if the above link fails) 
# !gdown --id '1qwjbRjq481lHsnTrrF4OjKQnxzgoLEFR' --output hw7_data.zip

# Download Link 3 (if the above link fails) 
# !gdown --id '1QXuWjNRZH6DscSd6QcRER0cnxmpZvijn' --output hw7_data.zip

!unzip -o hw7_data.zip

# For this HW, K80 < P4 < T4 < P100 <= T4(fp16) < V100
!nvidia-smi

#安装transformers
# You are allowed to change version of transformers or use other toolkits
!pip install transformers

#引入库,fix seed
import json
import numpy as np
import random
import torch
from torch.utils.data import DataLoader, Dataset 
from transformers import AdamW, BertForQuestionAnswering, BertTokenizerFast

from tqdm.auto import tqdm

device = "cuda" if torch.cuda.is_available() else "cpu"

# Fix random seed for reproducibility
def same_seeds(seed):
	  torch.manual_seed(seed)
	  if torch.cuda.is_available():
		    torch.cuda.manual_seed(seed)
		    torch.cuda.manual_seed_all(seed)
	  np.random.seed(seed)
	  random.seed(seed)
	  torch.backends.cudnn.benchmark = False
	  torch.backends.cudnn.deterministic = True
same_seeds(0)

# Change "fp16_training" to True to support automatic mixed precision training (fp16)	
#解读baseline的代码，暂时还不需要考虑这个fp16的部分
fp16_training = False

if fp16_training:
    !pip install accelerate==0.2.0
    from accelerate import Accelerator
    accelerator = Accelerator(fp16=True)
    device = accelerator.device

# Documentation for the toolkit:  https://huggingface.co/docs/accelerate/

#载入bert 的model 和 tokenizer
model = BertForQuestionAnswering.from_pretrained("bert-base-chinese").to(device)   #从transformers库中的pretrained好的model获取到这个中文版本的翻译 model
tokenizer = BertTokenizerFast.from_pretrained("bert-base-chinese")          #用于tokenize的对象

# You can safely ignore the warning message (it pops up because new prediction heads for QA are initialized randomly)

#从文件中把 数据 读取到 数组中
#这个部分就是定义1个读取数据的函数，然后调用这个函数，从3个json文件中读取对应的paragraphs 和 questions数据
#(1)先查看各个文件中的数据的类型和分布情况:
 #"questions": [
 #       {
 #           "id": 0,
 #           "paragraph_id": 660,
 #           "question_text": "福岡市的兩大中心地區指的是博多地區，還有哪一地區?",
 #           "answer_text": "天神地區",
 #           "answer_start": 343,
 #           "answer_end": 346
 #里面的questions数据就是1个map映射到1个数组，每个元素是上述这些，注意，每个quetion的id都不一样，对应于token_type_ids
 #paragraphs是1个map映射到1个数组，每个元素都是1串文字，每一串都是1篇文章，没有其他东西了，所以应该是用上面的paragraphs_id去找

def read_data(file):
    with open(file, 'r', encoding="utf-8") as reader:
        data = json.load(reader)
    return data["questions"], data["paragraphs"]

train_questions, train_paragraphs = read_data("hw7_train.json")
dev_questions, dev_paragraphs = read_data("hw7_dev.json")
test_questions, test_paragraphs = read_data("hw7_test.json")

#将原始的数据 进行 tokenizer
# Tokenize questions and paragraphs separately
# 「add_special_tokens」 is set to False since special tokens will be added when tokenized questions and paragraphs are combined in datset __getitem__ 
#这个部分估计就是用上述的bert_tokenizer来对这些数据中的"中文字"进行tokenize了


train_questions_tokenized = tokenizer([train_question["question_text"] for train_question in train_questions], add_special_tokens=False)
dev_questions_tokenized = tokenizer([dev_question["question_text"] for dev_question in dev_questions], add_special_tokens=False)
test_questions_tokenized = tokenizer([test_question["question_text"] for test_question in test_questions], add_special_tokens=False) 

#这段代码的作用无非就是 利用tokenizer这个对象处理 对上面的3组数据进行挨个地处理罢了:
#上面也就是对train_question数组中的每一项中的"question_text"中的《中文文字内容进行tokenizer》之后，只是将这一段文字的tokens存储到train_questions_tokenized这个数组中

train_paragraphs_tokenized = tokenizer(train_paragraphs, add_special_tokens=False)
dev_paragraphs_tokenized = tokenizer(dev_paragraphs, add_special_tokens=False)
test_paragraphs_tokenized = tokenizer(test_paragraphs, add_special_tokens=False)
#这一段也是上面一样的作用，也是将文字转换为tokens之后保存到对应的数组中

# You can safely ignore the warning message as tokenized sequences will be futher processed in datset __getitem__ before passing to model

#获取 train_loader,dev_loader,test_loader:
class QA_Dataset(Dataset):
    def __init__(self, split, questions, tokenized_questions, tokenized_paragraphs): #参数split对象，QA分别的tokens数组，还有1个questions不知道是什么
        self.split = split                             #split == 'train' of 'Dev'
        self.questions = questions
        self.tokenized_questions = tokenized_questions
        self.tokenized_paragraphs = tokenized_paragraphs
        self.max_question_len = 40
        self.max_paragraph_len = 150
        
        ##### TODO: Change value of doc_stride #####
        self.doc_stride = 150

        # Input sequence length = [CLS] + question + [SEP] + paragraph + [SEP]
        self.max_seq_len = 1 + self.max_question_len + 1 + self.max_paragraph_len + 1

    def __len__(self):
        return len(self.questions)       #需要提问的数量，所以，这个questions到底是什么呢

    def __getitem__(self, idx):
        question = self.questions[idx]
        tokenized_question = self.tokenized_questions[idx]
        tokenized_paragraph = self.tokenized_paragraphs[question["paragraph_id"]] #从这里可以看出这个questions就是存储有结构体的questions原始内容
        #上面已经完成了__getitem__中的基本内容，可以返回tokenized_que 和 对应的paragraph_tokens
        #下面就是一些对这些数据进行预处理的内容，为了方便得到更加nice的训练数据

        ##### TODO: Preprocessing #####
        # Hint: How to prevent model from learning something it should not learn

        if self.split == "train":
            # Convert answer's start/end positions in paragraph_text to start/end positions in tokenized_paragraph 
            #这里的tokenized_paragraph就是1个文段而已，这2行代码的作用就是
            #首先，这个question['answer_start']得到的就是一个数值，这个数值代表再对应文章中的其实的位置 
            #通过这2行代码得到 分词之后的 索引位置
            answer_start_token = tokenized_paragraph.char_to_token(question["answer_start"])
            answer_end_token = tokenized_paragraph.char_to_token(question["answer_end"])

            # A single window is obtained by slicing the portion of paragraph containing the answer

            #这个部分就是助教说的可以修改的部分，因为这里的删减，导致了 一些信息的 丢失,如果修改这个preprocess部分，应该可以提高正确率
            mid = (answer_start_token + answer_end_token) // 2  
            paragraph_start = max(0, min(mid - self.max_paragraph_len // 2, len(tokenized_paragraph) - self.max_paragraph_len)) #由于有最长的paragraph的长度限制，所以开始的位置取0，或者后面合理的一个位置
            paragraph_end = paragraph_start + self.max_paragraph_len  #end的位置就是start + max_len咯
            
            # Slice question/paragraph and add special tokens (101: CLS, 102: SEP)<————其实这里将input_que和input_para相加就得到了左边这个窗口，也就是bert的输入窗口
            input_ids_question = [101] + tokenized_question.ids[:self.max_question_len] + [102]  #这里面就是ids--相当于的一个文字的替代数值，
            input_ids_paragraph = tokenized_paragraph.ids[paragraph_start : paragraph_end] + [102]#paragraph_input_token数组的设置
            
            # Convert answer's start/end positions in tokenized_paragraph to start/end positions in the window  
            answer_start_token += len(input_ids_question) - paragraph_start #如果我没有想错的话，就是将CLS+question + sep +paragraph+sep拼接的位置
            answer_end_token += len(input_ids_question) - paragraph_start
            
            # Pad sequence and obtain inputs to model 
            input_ids, token_type_ids, attention_mask = self.padding(input_ids_question, input_ids_paragraph) #返回input的ids 和 token_type_ids,mask下面查看一下这个padding函数的作用
            return torch.tensor(input_ids), torch.tensor(token_type_ids), torch.tensor(attention_mask), answer_start_token, answer_end_token

        # Validation/Testing
        else:
            input_ids_list, token_type_ids_list, attention_mask_list = [], [], []
            
            # Paragraph is split into several windows, each with start positions separated by step "doc_stride"
            #这里返回的是好几个list，也就是说，这些内容之间起点的位置相隔为doc_stride,也就是相当于 不同窗口之间的有doc_stride部分不相交
            for i in range(0, len(tokenized_paragraph), self.doc_stride):
                
                # Slice question/paragraph and add special tokens (101: CLS, 102: SEP)
                input_ids_question = [101] + tokenized_question.ids[:self.max_question_len] + [102]
                input_ids_paragraph = tokenized_paragraph.ids[i : i + self.max_paragraph_len] + [102]
                
                # Pad sequence and obtain inputs to model
                input_ids, token_type_ids, attention_mask = self.padding(input_ids_question, input_ids_paragraph)
                
                input_ids_list.append(input_ids)
                token_type_ids_list.append(token_type_ids)
                attention_mask_list.append(attention_mask)
            
            return torch.tensor(input_ids_list), torch.tensor(token_type_ids_list), torch.tensor(attention_mask_list)

    #下面分析一下这个padding函数的作用,其实就是那个研二的学长在讲transformer时候提到的长度不够，需要补齐padding1的功能
    #其实这里最好是联系那个 CSL + question_tokens + SEP + para_tokens + SEP的那个transformer的输入窗口进行理解

    def padding(self, input_ids_question, input_ids_paragraph):
        # Pad zeros if sequence length is shorter than max_seq_len
        padding_len = self.max_seq_len - len(input_ids_question) - len(input_ids_paragraph)
        # Indices of input sequence tokens in the vocabulary
        input_ids = input_ids_question + input_ids_paragraph + [0] * padding_len

        #token_type_ids就是用来  标注出其中的para的位置（不过它原来的作用是区分不同的 句子）
        # Segment token indices to indicate first and second portions of the inputs. Indices are selected in [0, 1]
        token_type_ids = [0] * len(input_ids_question) + [1] * len(input_ids_paragraph) + [0] * padding_len
        
        #将padding部分的mask设置为0，非padding1的部分设置为1
        # Mask to avoid performing attention on padding token indices. Mask values selected in [0, 1]
        attention_mask = [1] * (len(input_ids_question) + len(input_ids_paragraph)) + [0] * padding_len
        
        return input_ids, token_type_ids, attention_mask

train_set = QA_Dataset("train", train_questions, train_questions_tokenized, train_paragraphs_tokenized)
dev_set = QA_Dataset("dev", dev_questions, dev_questions_tokenized, dev_paragraphs_tokenized)
test_set = QA_Dataset("test", test_questions, test_questions_tokenized, test_paragraphs_tokenized)

train_batch_size = 32

# Note: Do NOT change batch size of dev_loader / test_loader !
# Although batch size=1, it is actually a batch consisting of several windows from the same QA pair
train_loader = DataLoader(train_set, batch_size=train_batch_size, shuffle=True, pin_memory=True)
dev_loader = DataLoader(dev_set, batch_size=1, shuffle=False, pin_memory=True)
test_loader = DataLoader(test_set, batch_size=1, shuffle=False, pin_memory=True)

#定义1个eval处理的部分：
def evaluate(data, output): #这个data就是dev_loader中的每个元素，也就是那3组数据， out_put就是将data输入到bert的结果
    ##### TODO: Postprocessing #####
    # There is a bug and room for improvement in postprocessing 
    # Hint: Open your prediction file to see what is wrong 
    
    answer = ''
    max_prob = float('-inf')
    num_of_windows = data[0].shape[1]
    
    for k in range(num_of_windows):
        # Obtain answer by choosing the most probable start position / end position
        start_prob, start_index = torch.max(output.start_logits[k], dim=0) #获得最大可能的起始index 和 对应的probablility
        end_prob, end_index = torch.max(output.end_logits[k], dim=0)    #获取最大可能的结尾index 和 对应的probablility
        
        # Probability of answer is calculated as sum of start_prob and end_prob
        prob = start_prob + end_prob                    #相加作为总prob
        
        # Replace answer if calculated probability is larger than previous windows
        if prob > max_prob:
            max_prob = prob
            # Convert tokens to chars (e.g. [1920, 7032] --> "大 金")
            answer = tokenizer.decode(data[0][0][k][start_index : end_index + 1])
    
    # Remove spaces in answer (e.g. "大 金" --> "大金")
    return answer.replace(' ','')

#train里面的代码
num_epoch = 1
validation = True
logging_step = 100      #每隔logging_step进行1次输出
learning_rate = 1e-4
optimizer = AdamW(model.parameters(), lr=learning_rate)

if fp16_training:
    model, optimizer, train_loader = accelerator.prepare(model, optimizer, train_loader) 

model.train()

print("Start Training ...")

for epoch in range(num_epoch):
    step = 1
    train_loss = train_acc = 0
    
    for data in tqdm(train_loader):	 
        # Load all data into GPU
        data = [i.to(device) for i in data]
        
        # Model inputs: input_ids, token_type_ids, attention_mask, start_positions, end_positions (Note: only "input_ids" is mandatory)
        # Model outputs: start_logits, end_logits, loss (return when start_positions/end_positions are provided)
        #这个bert模型的输出都已经是封装好的了，所以loss也在里面了  
        output = model(input_ids=data[0], token_type_ids=data[1], attention_mask=data[2], start_positions=data[3], end_positions=data[4])

        # Choose the most probable start position / end position
        start_index = torch.argmax(output.start_logits, dim=1)
        end_index = torch.argmax(output.end_logits, dim=1)
        
        # Prediction is correct only if both start_index and end_index are correct
        train_acc += ((start_index == data[3]) & (end_index == data[4])).float().mean()
        train_loss += output.loss

        
        if fp16_training:
            accelerator.backward(output.loss)
        else:
            output.loss.backward()
        
        optimizer.step()
        optimizer.zero_grad()
        step += 1

        ##### TODO: Apply linear learning rate decay #####
        
        
        # Print training loss and accuracy over past logging step
        if step % logging_step == 0:
            print(f"Epoch {epoch + 1} | Step {step} | loss = {train_loss.item() / logging_step:.3f}, acc = {train_acc / logging_step:.3f}")
            train_loss = train_acc = 0

    if validation:
        print("Evaluating Dev Set ...")
        model.eval()
        with torch.no_grad():
            dev_acc = 0
            for i, data in enumerate(tqdm(dev_loader)):
                output = model(input_ids=data[0].squeeze(dim=0).to(device), token_type_ids=data[1].squeeze(dim=0).to(device),
                       attention_mask=data[2].squeeze(dim=0).to(device))
                # prediction is correct only if answer text exactly matches
                dev_acc += evaluate(data, output) == dev_questions[i]["answer_text"] #如果返回的结果就是ans，那么dev_acc+1
            print(f"Validation | Epoch {epoch + 1} | acc = {dev_acc / len(dev_loader):.3f}")
        model.train()

# Save a model and its configuration file to the directory 「saved_model」 
# i.e. there are two files under the direcory 「saved_model」: 「pytorch_model.bin」 and 「config.json」
# Saved model can be re-loaded using 「model = BertForQuestionAnswering.from_pretrained("saved_model")」
print("Saving Model ...")
model_save_dir = "saved_model" 
model.save_pretrained(model_save_dir)

#test部分的内容：
print("Evaluating Test Set ...")

result = []

model.eval()
with torch.no_grad():
    for data in tqdm(test_loader):
        output = model(input_ids=data[0].squeeze(dim=0).to(device), token_type_ids=data[1].squeeze(dim=0).to(device),
                       attention_mask=data[2].squeeze(dim=0).to(device))
        result.append(evaluate(data, output))

result_file = "result.csv"
with open(result_file, 'w') as f:	
	  f.write("ID,Answer\n")
	  for i, test_question in enumerate(test_questions):
        # Replace commas in answers with empty strings (since csv is separated by comma)
        # Answers in kaggle are processed in the same way
		    f.write(f"{test_question['id']},{result[i].replace(',','')}\n")

print(f"Completed! Result is in {result_file}")

version2：改进版本

1.改进那个learning rate decay部分：

torch.optim — PyTorch 2.0 documentation

optimizer = optim.SGD(model.parameters(), lr=0.01, momentum=0.9)
scheduler = ExponentialLR(optimizer, gamma=0.9)

for epoch in range(20):
    for input, target in dataset:
        optimizer.zero_grad()
        output = model(input)
        loss = loss_fn(output, target)
        loss.backward()
        optimizer.step()
    scheduler.step()  #每隔epoch调用1次(如果我只有1个epoch呢？)

另一种2次decay:

optimizer = optim.SGD(model.parameters(), lr=0.01, momentum=0.9)
scheduler1 = ExponentialLR(optimizer, gamma=0.9)
scheduler2 = MultiStepLR(optimizer, milestones=[30,80], gamma=0.1)

for epoch in range(20):
    for input, target in dataset:
        optimizer.zero_grad()
        output = model(input)
        loss = loss_fn(output, target)
        loss.backward()
        optimizer.step()
    scheduler1.step()
    scheduler2.step()

2.减少doc_step的数值：

第一次改为75 + decay_gamma=0.99->效果如下：（kaggle）

colab：

效果非常不错！！！嘻嘻！！在Dev上表现有显著提升

备注：在kaggle上下载数据改成如下：

!pip install gdown
import gdown
url = 'https://drive.google.com/uc?id=1AVgZvy3VFeg0fX-6WQJMHPVrx3A-M1kb'
output = 'hw7_data.zip'
gdown.download(url, output, quiet=False)

 

version3:使用hugging_face上的pretrained_model

第一点，修改dataloader中input_para的start和end的位置，使得ans_start 和 ans_end并不总是处于这个para的中间位置，（总是处于中间的话，会让model产生误解，以为ans总是处于窗口中间），不过，这里怎么进行修改呢？

答：主要是修改para_start和ans_start的距离，这样，就可以让ans_start处于窗口的不同位置

(......目前没有进行修改，我想用概率的方法应该比较容易实现，以后再说吧 ...)

第二点，改用其他model:

(1)

hfl/chinese-pert-base-mrc · Hugging Face

# Load model directly
from transformers import AutoTokenizer, AutoModelForQuestionAnswering

tokenizer = AutoTokenizer.from_pretrained("hfl/chinese-pert-base-mrc")
model = AutoModelForQuestionAnswering.from_pretrained("hfl/chinese-pert-base-mrc").to(device)

#很多时候，报错就是因为 忘记了to(device)

我里个去，Hugging_face上面的pretrained model就是好用！！！！无敌了老哥

直接吊打一切

(2)

这个model也还行，不过比起上面那个，还是拉了一些

(我当时忘了他说要用berttokenizerFast了)

ckiplab/bert-base-chinese-qa · Hugging Face

# Load model directly
from transformers import AutoTokenizer, AutoModelForQuestionAnswering

tokenizer = AutoTokenizer.from_pretrained("ckiplab/bert-base-chinese-qa")
model = AutoModelForQuestionAnswering.from_pretrained("ckiplab/bert-base-chinese-qa").to(device)