shop_list = [     ('iphone',8888),     ('iMac Pro',10888),     ('Tesila',200000),     ('bike',1020),     ('mibook',1001) ] shopping_list = [] salary = input('请输入你的工资>>>:') if salary.isdigit():     salary = int(salary)     while True:         for index,item in enumerate(shop_list,1):             print(index,item)         user_choice = input('请输入要选择的商品序号>>>:')         if user_choice.isdigit():             user_choice = int(user_choice)             if user_choice <= len(shop_list) and user_choice > 0:                 p_item = shop_list[user_choice -1 ]                 shopping_list.append(p_item)                 if p_item[1] <= salary:                     salary -= p_item[1]                     print('你购买的商品为%s，剩余金额为%s'%(p_item,salary))         elif user_choice == 'q':             for l_item in shopping_list:                 print('---shopping list---',l_item,'\n还剩%s$'%(salary))                 break         else:             print('输入有错误，请重新输入!') else:     print('输入有错误，请重新输入!')