基本Python寫法：超市算術

＃首先我們給個list

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

＃定義Dictionary

stock = {
    "banana": 6,
    "apple": 0,
    "orange": 32,
    "pear": 15
}
   
prices = {
    "banana": 4,
    "apple": 2,
    "orange": 1.5,
    "pear": 3
}

# 定義函數，裡面有個變數food，然後利用條件式，如果有庫存就加進總計，庫存減一

def compute_bill(food):
    total= 0
    for number in food:
        if stock[number] > 0:
            total += prices[number]
            stock[number] -= 1
    return total