老男孩培訓練習購買商品

#!/usr/bin/env python
#-*-coding=utf-8 -*-
#AUTHOR:duwentao

product_list = [
    ('Iphone',5000),
    ('book',10),
    ('watch',10600),
    ('bike',800),
]

shopping_list=[]

#判斷工資是否爲數字
salary = input("請輸入你的工資：")
if salary.isdigit():
    salary = int(salary)

while True:
    for item in product_list:
        print (product_list.index(item),item)

    user_choice = input('請輸入你要購買的商品號：')
    if user_choice.isdigit():
        user_choice = int(user_choice)

        if user_choice >= 0 and user_choice < len(product_list):
            p_item = product_list[user_choice]

            if p_item[1] > salary:
                print('餘額不足')
            else:
                shopping_list.append(item)
                salary  -=  p_item[1]
                print('你已經購買了%s,您的餘額爲%s' %(item,salary))

        else:
            print('你購買的商品不存在')
    elif user_choice == 'q':
        print ('----shopping list----')
        for p in shopping_list:
            print(p)
        print('你的餘額爲',salary)
        exit()


    else:
        print ("輸入有誤，請從新編號")
        print ("正在退出")
        exit()