salary = input('input your salary:')
if salary.isdigit:
  salary = int(salary)
else:
  exit('salary is not digit!!')
welcome_msg = 'welcome to our shoping mall'
print(welcome_msg.center(50,'-'))
product_list = [
  ('Iphone',5888),
  ('Mac Air',8000),
  ('XiaoMi',19.9),
  ('coffee',30),
  ('Tesla',820000),
  ('Bike',700),
  ('Cloth',200)
]
shop_car = []
#推出标志位
exit_flag = 0
while exit_flag is not True:
  print('product list :'.center(50,'-'))
  for item in enumerate(product_list):
    index = item[0]   #获得商品序号
    p_name = item[1][0]  #获得商品名称
    p_price= item[1][1]  #获得商品价格
    print(index,p_name,p_price)
  user_choice = input('[q=quit,c=check] what do you want to buy?:')
  if user_choice.isdigit():
    user_choice = int(user_choice)
    if user_choice < len(product_list): #输入的商品序号要在范围之内
      p_item = product_list[user_choice] #选择的商品
      if p_item[1] <= salary: #买得起
        shop_car.append(p_item) #放入购物车
        salary -= p_item[1] #减钱
        print('purchased products are:'.center(40, '-'))
        for item in shop_car:
          print(item)
        print('Your balance is [%s]' % salary)
      else:          #买不起
        print('Your balance is [%s],cannot buy the product!'%salary)
    else:
      print('we do not have the product,please input again!')
  elif user_choice == 'q' or user_choice == 'quit':
    print('purchased products are:'.center(40,'-'))
    for item in shop_car:
      print(item)
    print('END '.center(40,'-'))
    print('Your balance is [%s]'%salary)
    exit_flag =True
  elif user_choice == 'c' or user_choice == 'check':
    print('purchased products are:'.center(40, '-'))
    for item in shop_car:
      print(item)
    print('Your balance is %d' % salary)
    print('Check '.center(40, '-'))
  else:
    print('Incorrect input ,please input again!!')

input your salary:10000
-----------welcome to our shoping mall------------
------------------product list :------------------
0 Iphone 5888
1 Mac Air 8000
2 XiaoMi 19.9
3 coffee 30
4 Tesla 820000
5 Bike 700
6 Cloth 200
[q=quit,c=check] what do you want to buy?:0
added [[('Iphone', 5888)]] into shop car ,yourcurrent balence is 4112
------------------product list :------------------
0 Iphone 5888
1 Mac Air 8000
2 XiaoMi 19.9
3 coffee 30
4 Tesla 820000
5 Bike 700
6 Cloth 200
[q=quit,c=check] what do you want to buy?:1
Your balance is [4112],cannot buy the product!
------------------product list :------------------
0 Iphone 5888
1 Mac Air 8000
2 XiaoMi 19.9
3 coffee 30
4 Tesla 820000
5 Bike 700
6 Cloth 200
[q=quit,c=check] what do you want to buy?:c
shop car list are [[('Iphone', 5888)]],your balance is 4112
------------------product list :------------------
0 Iphone 5888
1 Mac Air 8000
2 XiaoMi 19.9
3 coffee 30
4 Tesla 820000
5 Bike 700
6 Cloth 200
[q=quit,c=check] what do you want to buy?:4
Your balance is [4112],cannot buy the product!
------------------product list :------------------
0 Iphone 5888
1 Mac Air 8000
2 XiaoMi 19.9
3 coffee 30
4 Tesla 820000
5 Bike 700
6 Cloth 200
[q=quit,c=check] what do you want to buy?:q
--------purchased products are:---------
('Iphone', 5888)
------------------END ------------------
Your balance is [4112]
Process finished with exit code 0

>>> print('product list :'.center(50,'-'))
------------------product list :------------------

>>> for item in enumerate(product_list):
print(item)
(0, ('Iphone', 5888))
(1, ('Mac Air', 8000))
(2, ('XiaoMi', 19.9))
(3, ('coffee', 30))
(4, ('Tesla', 820000))
(5, ('Bike', 700))
(6, ('Cloth', 200))