写代码了

#__author: Administrator
#date: 2016/8/23

product_list=[
('Mac',9000),
('kindle',800),
('tesla',900000),
('python book',105),
('bike',2000),

]
saving=input('please input your money:')
shopping_car=[]
if saving.isdigit():
saving=int(saving)
while True:
#打印商品内容
for i,v in enumerate(product_list,1):
print(i,'>>>>',v)

#引导用户选择商品
choice=input('选择购买商品编号[退出：q]：')

#验证输入是否合法
if choice.isdigit():
choice=int(choice)
if choice>0 and choice<=len(product_list):
#将用户选择商品通过choice取出来
p_item=product_list[choice-1]

#如果钱够，用本金saving减去该商品价格，并将该商品加入购物车
if p_item[1]<saving:
saving-=p_item[1]

shopping_car.append(p_item)

else:
print('余额不足，还剩%s'%saving)
print(p_item)
else:
print('编码不存在')
elif choice=='q':
print('------------您已经购买如下商品----------------')
#循环遍历购物车里的商品，购物车存放的是已买商品
for i in shopping_car:
print(i)
print('您还剩%s元钱'%saving)
break
else:
print('invalid input')