购物车小程序（while循环，列表）

 while True:
     salary = input("please input your salary:")
     if salary.isdigit():
         salary=int (salary)
         break
     else:
         print("Invalid input! please input a number:")

 product_cart = [['iphone6s',5800],                 #定义商品列表
                 ['macbook',9000],
                 ['coffee',30],
                 ['python book',80],
                 ['bicycle',1500]
                 ]
 shopping_cart = []                                 #定义购物车
 balance=salary

 while True:
     for i,v in  enumerate(product_cart,1):         #enumerate参数将商品列表循环打印，并且第一行从1开始 加上序号
         print(i,v)

     choise = input("please input your selection[typing 'q' to quit]:")
     if choise.isdigit():                           #判断是否是数字
         choise=int(choise)
         if choise >=1 and choise<=len(product_cart): #判断输入的字符是否符合商品列表所在的范围
             sales =product_cart[choise-1]            #将用户选择的商品赋值给sales
             if balance >=sales[1]:                   #判断余额是否足够购买该商品
                 balance -=sales[1]                   #购买完后将余额减去商品价格
                 shopping_cart.append(sales)          #将商品加入购物车
                 print("your balance is %s :"%balance)
                 print()
             else:
                 print("your balance is %s,not enough to buy this one，please try another products!"%balance,)
                 print()

         else:
             print("no such a selection")
     elif choise == 'q':                            #判断是否是q选择退出
         print("your shopping cart is:")
         for i, v in enumerate(shopping_cart, 1):
             print(i, v)
         break
     else:
         print("Invalid typing.please typing a number!") #非数字执行的操作