instance 1:shopping cart

#! /usr/bin/env python
# -*- coding: utf-8 -*-
# __author__ = "Deakin"
# Email: 469792427@qq.com
# Date: 2018/1/2

#程序：购物车程序

#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

product_list=[
    ("iphone",8000),
    ("computer",6000),
    ("car",30000),
    ("coffee",30),
    ("watch",500),
    ("book",80),
]
shopping_list=[]
salary=input("please key in your salary:")
if salary.isdigit():
    salary=int(salary)
    while True:
        #for item in product_list:
            #print(product_list.index(item),item)
        #break
        for index,item  in enumerate(product_list):
            print(index,item)
        print("选择要购买的商品编号，按q退出")
        user_choice=input("选择要购买的商品：")
        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]
                if p_item[1]<=salary:#买得起
                    shopping_list.append(p_item)
                    salary-=p_item[1]
                    print("added %s into shopping cart,your current balance is \033[31;1m%s\033[0m"%(p_item,salary))
                else:#买不起
                    print("\033[41;1m穷逼，你的余额只有%s了,还不赶紧充钱\033[0m"%(salary))
            else:
                print("the product is not exist")

        elif  user_choice==‘q‘:
            print("-------shopping list-------")
            for p in shopping_list:
                print(p)
            print("your balance is :",salary)
            exit()
        else:
            print("invalid opation")