loop元组列表 - TypeError：不可用类型：＆＃39; list＆＃39;

Question

这有效：

shopping_list = ["banana", "orange", "apple"]

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

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

def compute_bill(food):
    total = 0
   # food = tuple(food)
    for food in food:
        total += prices[food]

    return total 

print compute_bill(shopping_list) 

但是如果我把食物转换成循环中的任何其他东西，例如X - 食物中的x - 那么python会给我以下错误（它只适用于食物中的食物。）

Traceback (most recent call last):
  File "compute-shopping.py", line 25, in <module>
    print compute_bill(shopping_list) 
  File "compute-shopping.py", line 21, in compute_bill
    total += prices[food]
TypeError: unhashable type: 'list'

这与使用元组或列表作为字典的关键字无关......或者是它？！

Answer 1

假设食物是一个列表，您只需要将for循环更改为：

for food_type in food:
    total += prices[food_type]