Python ValueError报错求助：too many values to unpack (expected 3)

运行测试代码时触发报错：ValueError: too many values to unpack (expected 3)，相关代码如下：

BookDict 类代码 #

class BookDict:
    def __init__(self, filename):
        self.my_dict = {}
        with open(filename) as f:
            for line in f:
                title, author, ratings = line.strip().split(",")
                ratings = [float(rating) for rating in ratings.split(";")]
                self.my_dict[title] = Book(author, title, ratings)

    def lookup(self, title_string_some):
        if title_string_some in self.my_dict:
            book = self.my_dict[title_string_some]
            print(f"{book} ({book.average_rating():.2f})")
            return book
        else:
            print("Not Found")
            return None

测试代码 #

my_bookdict = BookDict('books2.csv')
my_book = my_bookdict.lookup('Pride and Prejudice')
book2 = my_bookdict.lookup('Erehwon')

核心原因 #

报错出现在title, author, ratings = line.strip().split(",")这一行：当books2.csv中存在带逗号的字段（比如书名"Pride and Prejudice, A Classic"），直接用split(",")会把该字段拆成多个部分，导致分割后得到的元素数量大于3，无法匹配三个变量的解包要求。

修复代码 #

改用Python标准库csv模块处理CSV文件，它能正确解析带引号包裹的含逗号字段，同时添加异常处理避免格式错误导致崩溃：

import csv

class BookDict:
    def __init__(self, filename):
        self.my_dict = {}
        with open(filename, newline='', encoding='utf-8') as f:
            # 使用csv.reader解析文件，自动处理带引号的字段
            reader = csv.reader(f)
            for row in reader:
                # 跳过格式不符的行
                if len(row) != 3:
                    print(f"跳过无效行: {row}")
                    continue
                title, author, ratings_str = row
                try:
                    # 转换评分为浮点型列表
                    ratings = [float(rating) for rating in ratings_str.split(";")]
                except ValueError:
                    print(f"{title} 的评分格式错误，跳过该行")
                    continue
                self.my_dict[title] = Book(author, title, ratings)

    def lookup(self, title_string_some):
        if title_string_some in self.my_dict:
            book = self.my_dict[title_string_some]
            print(f"{book} ({book.average_rating():.2f})")
            return book
        else:
            print("Not Found")
            return None

额外优化说明 #

1. csv.reader会自动识别被引号包裹的字段，不会错误分割含逗号的内容；
2. 添加行长度检查和评分转换异常捕获，遇到无效数据时程序不会直接崩溃，而是给出提示并跳过；
3. 指定encoding='utf-8'避免中文或特殊字符的编码问题。

内容的提问来源于stack exchange，提问作者Craig Fu