我有两个字典，我需要将它们相乘并得到它们的总和，这两个字典都有相同的键(我需要一些项目的库存和价格的总和)。
# 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}
# Get the values from stock and price for each menu item and multiply by eachother
for key in price:
menu_stock = price[key] * stock[key]
# Get the sum of these values
total_stock_worth = sum(menu_stock)
# Print statement with the calculated total stock worth
print("The total stock worth is £" + str("{:.2f}".format(total_stock_worth)))
我得到错误消息(对于第12行：total_stock_worth=sum(menu_stock))：TypeError:"float"对象不是可迭代的
我想要的输出是：总股票价值为131.00英镑
menu_stock(在循环中)存储float值，而sum函数要求其参数为可迭代
因此，在计算它们的和之前，您需要累积price*stocks的所有乘积。
sum函数与iterable一起工作，例如：list, set等。在您的代码中，menu_stock是float，而不是iterable。要解决您的问题，请将menu_stock声明为列表，并将append声明为stock和price的乘积。循环结束后，调用sum函数来计算total_stock_worth。
此外，您不需要调用str()方法，format()会自动为您执行此操作。
解决方案
# 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}
# declare menu_stock as list
menu_stock = []
# Get the values from stock and price for each menu item and multiply by eachother
for key in price:
menu_stock.append(price[key] * stock[key])
# Get the sum of these values
total_stock_worth = sum(menu_stock)
# Print statement with the calculated total stock worth
print("The total stock worth is £{:.2f}".format(total_stock_worth))
要计算total_stock_worth，请尝试：
# 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}
# Get the values from stock and price for each menu item and multiply by eachother
total_stock_worth = sum(price[m] * stock[m] for m in menu)
# Print statement with the calculated total stock worth
print("The total stock worth is £" + str("{:.2f}".format(total_stock_worth)))
打印：
The total stock worth is £131.00
您有两个选项：
- 使用
for循环，并用+=递增total_stock_worth；或 - 将
sum( )与生成器表达式一起使用
在你的代码中，你试图混合两者，但失败的原因有两个：
- 您对单个值而不是一系列值调用
sum - 每次写入
total_stock_worth = ...时，都会擦除之前存储在total_stock_worth中的值
下面，两个选项：
# 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}
# OPTION 1: USE A FOR-LOOP AND INCREMENT MANUALLY
total_stock_worth = 0
for key in price:
menu_stock = price[key] * stock[key]
total_stock_worth = total_stock_worth + menu_stock
print("The total stock worth is £{:.2f}".format(total_stock_worth))
# OPTION 2: USE SUM() WITH A GENERATOR-EXPRESSION
total_stock_worth = sum(price[key] * stock[key] for key in price)
print("The total stock worth is £{:.2f}".format(total_stock_worth))
两个选项的输出相同：
The total stock worth is £131.00
根据个人喜好，您可以替换：
total_stock_worth = total_stock_worth + menu_stock
带有：
total_stock_worth += menu_stock
其中CCD_ 26可以被读取为"0"；增量"；；这两条线实际上是等价的。