购物车的实现

需求:
启动程序后，让用户输入工资，然后打印商品列表
允许用户根据商品编号购买商品
用户选择商品后，检测余额是否够，够就直接扣款，不够就提醒 
可随时退出，退出时，打印已购买商品和余额

#Author：liubin
goods_list=[('iphone',5000),
            ('clothing',1000),
            ('book',100),
            ('coffee',50),
            ('tea',200),
            ]
shopping_list = []
salary = input("Input your salary:")
if salary.isdigit():   #Python isdigit() 方法检测字符串是否只由数字组成。
    salary = int(salary)  #如果工资是数字，使用int
    while True:
        for index,item in enumerate(goods_list):   #http://www.runoob.com/python/python-func-enumerate.html一句话就是把下标取出来
            #print(product_list.index(item),item)
            print(index,item)    #打印商品列表
        user_choice = input("选择要买嘛？>>>:")
        if user_choice.isdigit():
            user_choice = int(user_choice)
            if user_choice < len(goods_list) and user_choice >=0:
                p_item = goods_list[user_choice]   #通过下表把商品取出来
                if p_item[1] <= salary: #买的起
                    shopping_list.append(p_item)
                    salary -= p_item[1]  #减去商品价格所剩下的钱
                    print("Added %s into shopping cart,your current balance is \033[31;1m%s\033[0m" %(p_item,salary) )
                else:
                    print("\033[41;1m你的余额只剩[%s]\033[0m" % salary)
            else:
                print("product code [%s] is not exist!"% user_choice)
        elif user_choice == 'q':
            print("--------shopping list------")
            for p in shopping_list:
                print(p)
            print("Your current balance:",salary)
            exit()
        else:
            print("Invalid option")

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