需求如下：

1. 启动程序后，让用户输入工资，然后打印商品列表；
2. 允许用户根据商品编号购买商品；
3. 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；
4. 可随时退出，退出时，打印已购买商品和余额。

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:Andy Chen

product_list = [
    (‘Iphone‘,5800),
    (‘Mac Pro‘,9800),
    (‘Bike‘,800),
    (‘Watch‘,10600),
    (‘Coffee‘,31),
    (‘Alex Pyton‘,120),
]
shopping_list = []
salary = raw_input("Input your salary>>>:")
if salary.isdigit():
    salary = int(salary)
    while True:
        for index,item in enumerate(product_list):
            print (index,item)
        user_choice = raw_input("选择要买嘛>>>：")
        if user_choice.isdigit():
           user_choice = int(user_choice)
           if user_choice < len(product_list) and user_choice >=0:
               p_item = product_list[user_choice]  #通过下标选择的产品
               if p_item[1] <= salary:#买得起
                   shopping_list.append(p_item)   #购买的产品追加到购物车列表
                   salary -= p_item[1]    #减钱
                   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]钱啦，还买毛线啊\033[0m" %salary)
           else:
               print("product code %s is not exist!" % user_choice ) #产品不存在
        elif user_choice == ‘q‘:
            print("--------shopping list----------")
            for p in shopping_list:
                print(p)
            print("your current balance:",salary)
            exit()
        else:
            print("invalid option")  # 无效的选项

else:
    print("Error！")

购物车程序