product_list = [     ['iphone6s', 5800],     ['mac book', 9000],     ['coffee', 32],     ['python book', 80],     ['bicycle', 1500] ] shopping_cart = [] while True:     salary = input("Salary（整数） = ")     if salary.isdigit():         salary = int(salary)         break     else:         print('请输入正确的数字') while True:     for i, j in enumerate(product_list, 1):         print(i, j)     print('当前余额:', salary)     choice = input('请输入你想购买的商品编号【q退出】:')     if choice.isdigit():         choice = int(choice)         if 0 < choice < len(product_list) + 1:             if salary >= int(product_list[choice-1][1]):                 print(product_list[choice-1][0], '已经加入您的购物车，当前余额:', salary - int(product_list[choice-1][1]))                 shopping_cart.append(product_list[choice-1])                 salary = salary - int(product_list[choice - 1][1])             else:                 print('余额不足:', salary - int(product_list[choice-1][1]))         else:             print('编号错误')     elif choice == 'q':         print('   已购买商品    金额')         for i, j in enumerate(shopping_cart, 1):             print(i, j)         print('你的余额为:', salary, '元。欢迎再次光临!')         break     else:         print('请输入正确的信息')