Python同键字典值相乘求和报错：TypeError及正确结果需求

错误原因 #

第12行的sum(menu_stock)触发报错，因为menu_stock是每次循环计算出的单个浮点数（比如第一个循环得到4.50*6=27.0），而sum()函数要求传入可迭代对象（比如列表、生成器），无法直接对单个数值执行求和操作。

同时原代码存在逻辑漏洞：每次循环都会覆盖total_stock_worth变量，即便sum能正常运行，最终也只会得到最后一个商品的库存价值，而非所有商品的总价值。

修正方案 #

方案1：累加变量逐步求和 #

初始化一个总和变量，每次循环将单个商品的库存价值累加到总和中：

# Create a list "menu" with 4 items
menu = ["sandwich", "burger", "fish", "chips"]
# Create a dictionary "stock" with the stock value for each item in the menu
stock = {"sandwich" : 6, "burger" : 5, "fish" : 6, "chips" : 10}
# Create a dictionary "price" with the price for each item in the menu
price = {"sandwich" : 4.50, "burger" : 6.00, "fish" : 6.50, "chips" : 3.50}

total_stock_worth = 0  # 初始化总和为0
for key in price:
    # 计算单个商品库存价值并累加到总和
    total_stock_worth += price[key] * stock[key]

# Print statement with the calculated total stock worth
print("The total stock worth is £" + str("{:.2f}".format(total_stock_worth)))

方案2：生成器表达式一次性求和 #

用更简洁的写法，直接生成所有商品的库存价值序列，再通过sum()一次性求和：

# Create a list "menu" with 4 items
menu = ["sandwich", "burger", "fish", "chips"]
# Create a dictionary "stock" with the stock value for each item in the menu
stock = {"sandwich" : 6, "burger" : 5, "fish" : 6, "chips" : 10}
# Create a dictionary "price" with the price for each item in the menu
price = {"sandwich" : 4.50, "burger" : 6.00, "fish" : 6.50, "chips" : 3.50}

# 遍历所有键，计算乘积后生成序列并求和
total_stock_worth = sum(price[key] * stock[key] for key in price)

# Print statement with the calculated total stock worth
print("The total stock worth is £" + str("{:.2f}".format(total_stock_worth)))

两种方案运行后都会输出目标结果：The total stock worth is £131.00

内容的提问来源于stack exchange，提问作者mandykg