Python 为什么for循环返回None？

我正在代码学院做一个练习，反复浏览购物清单。 为什么以下代码结果在结果中返回额外的

None

shopping_list = ["banana","apple"]

stock = { "banana": 6,
    "apple": 0,
    "orange": 32,
    "pear": 15
}

prices = { "banana": 4,
    "apple": 2,
    "orange": 1.5,
    "pear": 3
}

# Write your code below!
def compute_bill(food):
    total = 0
    for x in food:
        print x
        total += prices[x]
compute_bill(shopping_list)

---

您需要使用

return

语句来获取函数

compute\u bill

的结果。您的函数将返回

None

。也许您的环境只是在函数运行后显示返回值#在下面编写代码！def compute_bill（food）：total=0表示食品中的x：print x total+=prices[x]返回total print“total:+str（compute_bill（shopping_list）），在本教程本节的第二个示例之后-。

shopping_list = ["banana","apple"]

stock = { "banana": 6,
    "apple": 0,
    "orange": 32,
    "pear": 15
}

prices = { "banana": 4,
    "apple": 2,
    "orange": 1.5,
    "pear": 3
}

# Write your code below!
def compute_bill(food):
    total = 0
    for x in food:
        print x
        total += prices[x]
    return total
print(compute_bill(shopping_list))