Python3宠物店折扣计算函数实现及交互式程序开发求助

需求说明 #

某宠物店执行如下折扣规则：客户购买1只及以上宠物，且至少购买5件非宠物商品时，可享受非宠物商品总价20%的折扣（宠物商品不参与折扣）。需完成以下任务：

• 实现函数def discount(prices, isPet, nItems)，该函数接收交易信息：prices[i]为第i件商品原价，isPet[i]标记该商品是否为宠物；
• 编写交互式程序，让收银员依次输入每件商品价格（输入-1作为终止符）、是否为宠物（输入Y/N），将输入存入列表后调用上述函数，展示折扣金额及最终应付金额。

现有代码 #

def discount(prices, isPet, nItems):
    i = 0
    petCost = 0
    pets = 0
    items = 0
    itemsCost = 0
    while i < nItems:
        if isPet[i]:
            petCost += prices[i]
            pets += 1
        else:
            itemsCost += prices[i]
            items += 1
        i += 1
    if pets >= 1 and items >= 5:
        print("You receive discount")
        discountAmount = 0.2 * itemsCost
        finalAmount = petCost + itemsCost - discountAmount
        print("Final amount is", finalAmount)

def negativeNumber(price):
    while price > -1:
        if price < -1:
            print("Invalid price")
            return True
        else:
            return False
    
def main():
    prices = []
    isPet = []
    while True:
        price = int(input("Enter Price(-1 to quit): "))
        if price > -1:
            prices.append(price)
            itemName = input("Name of Item:")
            choice = input("Is it a pet(Y/N)? ")
            if choice == 'Y' or choice == 'y':
                isPet.append(True)
            else:
                isPet.append(False)
            print("")
        else:
            break
    nItems = len(prices)
    negativeNumber(price)    
    discount(prices, isPet, nItems)
main()

代码问题修复与优化 #

现有代码存在逻辑错误与功能缺失，以下是修正后的完整实现：

1. 修复价格校验逻辑 #

原negativeNumber函数逻辑完全失效，替换为有效的价格校验函数，同时在输入阶段即时拦截无效数据：

def validate_price(price):
    if price < -1:
        print("无效价格：价格不能低于-1")
        return False
    return True

2. 完善折扣计算函数 #

原函数未输出折扣金额，且未处理不满足折扣条件的场景，优化后：

def discount(prices, isPet, nItems):
    pet_cost = 0
    pet_count = 0
    non_pet_cost = 0
    non_pet_count = 0
    
    for i in range(nItems):
        if isPet[i]:
            pet_cost += prices[i]
            pet_count += 1
        else:
            non_pet_cost += prices[i]
            non_pet_count += 1
    
    discount_amount = 0.0
    final_amount = pet_cost + non_pet_cost
    
    if pet_count >= 1 and non_pet_count >= 5:
        print("您可享受折扣")
        discount_amount = 0.2 * non_pet_cost
        final_amount = pet_cost + non_pet_cost - discount_amount
    
    print(f"折扣金额: {discount_amount:.2f}")
    print(f"最终应付金额: {final_amount:.2f}")

3. 优化交互式输入流程 #

将输入提示改为中文，删除冗余调用，同时增加非数字输入的异常处理：

完整优化后代码 #

def discount(prices, isPet, nItems):
    pet_cost = 0
    pet_count = 0
    non_pet_cost = 0
    non_pet_count = 0
    
    for i in range(nItems):
        if isPet[i]:
            pet_cost += prices[i]
            pet_count += 1
        else:
            non_pet_cost += prices[i]
            non_pet_count += 1
    
    discount_amount = 0.0
    final_amount = pet_cost + non_pet_cost
    
    if pet_count >= 1 and non_pet_count >= 5:
        print("您可享受折扣")
        discount_amount = 0.2 * non_pet_cost
        final_amount = pet_cost + non_pet_cost - discount_amount
    
    print(f"折扣金额: {discount_amount:.2f}")
    print(f"最终应付金额: {final_amount:.2f}")

def validate_price(price):
    if price < -1:
        print("无效价格：价格不能低于-1")
        return False
    return True

def main():
    prices = []
    isPet = []
    while True:
        try:
            price = int(input("请输入商品价格（输入-1结束录入）："))
            if not validate_price(price):
                continue
            if price == -1:
                break
            prices.append(price)
            # 若无需记录商品名称，可删除此行
            item_name = input("请输入商品名称：")
            choice = input("是否为宠物（Y/N）？")
            isPet.append(choice.strip().upper() == 'Y')
            print()
        except ValueError:
            print("无效输入：请输入有效的数字价格")
    
    nItems = len(prices)
    discount(prices, isPet, nItems)

if __name__ == "__main__":
    main()

功能说明 #

• 输入阶段：支持逐个录入商品信息，自动校验价格有效性，对非数字、低于-1的输入给出错误提示；
• 计算阶段：自动统计宠物与非宠物商品的数量及总价，满足折扣条件时自动计算20%优惠；
• 输出阶段：清晰展示折扣金额与最终应付金额，保留两位小数提升可读性。

内容的提问来源于stack exchange，提问作者pevans590