如何实现美妆自动售货机多数量商品添加及购物车总价计算？

我正在学习计算机科学入门课程，需要编写基础代码实现一款美妆自动售货机，目前遇到两个问题：

• 允许用户输入指定商品的购买数量（如购买2支lipstick而非1支）
• 计算购物车总价时需考虑商品购买数量（如2支lipstick+1盘eyeshadow总价应为18美元而非10美元）

现有代码可正常运行，但尚未完成结账（选项d）功能，我打算先解决这两个问题再继续开发。我的思路是新增一个字典并使用count+=1来统计商品数量，但不确定具体实现方式。现有代码如下：

makeup_cart = []

makeup = {'lipstick': 8.00, 'highlight': 9.00, 'eyeshadow': 2.00, 'foundation':11.00, 'eyeliner':5.00, 'bronzer':7.00, 'lipliner':7.00,'blush':5.00, 'mascara':8.00, 'lipgloss  ': 4.00 }

while True:
        print("\nMenu:")
        print("a = Display makeup list and prices")
        print("b = Add a makeup item to cart")
        print("c = View cart")
        print("d = Checkout")
        print("e = Exit")

        choice = input("Enter your choice (a-e): ")

        if choice == "a":
            print(makeup) # prints makeup dictionary
        elif choice == "b":
            item = input("Enter a makeup from the menu item to add: ") #prompts user to input for makeup to add to cart 
            makeup_cart.append(item) #adds item to cart
            print(f"your {item} has been added to the cart  ") 
            print (makeup_cart) # prints current cart
        elif choice == "c":
            if makeup_cart:
              print("Makeup Cart:")
              for item in makeup_cart: #prints items the user added into the cart as a list of items 
                print( item)
        else:
          print("The makeup cart is empty") # if user hasnt added anything then the cart will come up empty 

用字典统计商品数量确实是最合适的方案，下面是修改后的完整代码，同时解决了数量输入、总价计算问题，还补全了结账功能：

# 把购物车改成字典，键是商品名，值是购买数量
makeup_cart = {}

makeup = {'lipstick': 8.00, 'highlight': 9.00, 'eyeshadow': 2.00, 
          'foundation':11.00, 'eyeliner':5.00, 'bronzer':7.00, 
          'lipliner':7.00,'blush':5.00, 'mascara':8.00, 'lipgloss': 4.00 }

while True:
    print("\nMenu:")
    print("a = Display makeup list and prices")
    print("b = Add a makeup item to cart")
    print("c = View cart")
    print("d = Checkout")
    print("e = Exit")

    choice = input("Enter your choice (a-e): ").lower()

    if choice == "a":
        print("\nAvailable Makeup & Prices:")
        for item, price in makeup.items():
            print(f"- {item}: ${price:.2f}")
    elif choice == "b":
        item = input("Enter the makeup item name to add: ").lower()
        # 检查商品是否存在
        if item not in makeup:
            print(f"Sorry, {item} is not in our menu.")
            continue
        # 输入购买数量并校验
        while True:
            try:
                quantity = int(input(f"How many {item} would you like to buy? "))
                if quantity <= 0:
                    print("Please enter a positive number.")
                    continue
                break
            except ValueError:
                print("Please enter a valid number.")
        # 更新购物车字典
        if item in makeup_cart:
            makeup_cart[item] += quantity
        else:
            makeup_cart[item] = quantity
        print(f"Added {quantity} {item}(s) to your cart.")
    elif choice == "c":
        if makeup_cart:
            print("\nYour Makeup Cart:")
            total = 0
            for item, quantity in makeup_cart.items():
                price = makeup[item]
                subtotal = price * quantity
                total += subtotal
                print(f"- {item}: {quantity} x ${price:.2f} = ${subtotal:.2f}")
            print(f"Current Total: ${total:.2f}")
        else:
            print("The makeup cart is empty.")
    elif choice == "d":
        if not makeup_cart:
            print("Your cart is empty, nothing to checkout.")
            continue
        # 计算总价
        total_price = 0
        print("\nCheckout Summary:")
        for item, quantity in makeup_cart.items():
            price = makeup[item]
            subtotal = price * quantity
            total_price += subtotal
            print(f"- {item}: {quantity} x ${price:.2f} = ${subtotal:.2f}")
        print(f"\nFinal Total: ${total_price:.2f}")
        print("Thank you for your purchase!")
        # 结账后清空购物车
        makeup_cart.clear()
    elif choice == "e":
        print("Goodbye!")
        break
    else:
        print("Invalid choice, please enter a letter from a to e.")

关键改动说明 #

• 购物车结构优化：将makeup_cart从列表改为字典，直接关联商品名和购买数量，统计和计算更高效
• 数量输入逻辑：添加商品时先校验商品是否存在，再让用户输入数量，同时做了正整数校验，避免无效输入
• 购物车展示升级：查看购物车时不仅显示商品和数量，还实时计算每个商品的小计和当前总价
• 结账功能补全：遍历购物车字典，根据单价计算每个商品的小计和最终总价，结账后清空购物车
• 细节优化：统一了输入的大小写处理，格式化价格为两位小数，让输出更规范

内容的提问来源于stack exchange，提问作者Abi