product_list = [ ('Iphone',8000), ('Mac Pro',9800), ('Bike',800), ('Watch',10600), ('Coffee',30), ] shopping_list = [] salary = input("Input your salary:") if salary.isdigit(): salary = int(salary) while True: for index,item in enumerate(product_list): print(index,item) user_choice = input("选择要买吗?>>>:") if user_choice.isdigit(): user_choice = int(user_choice) if user_choice < len(product_list) and user_choice >=0: p_item = product_list[user_choice] if p_item[1] <=salary: shopping_list.append(p_item) salary -= p_item[1] print("Your current balance:",salary) else: print("余额不足") else: print("product code [%s] is not exist!"% user_choice) elif user_choice =='q': print("-----shopping list------") print(shopping_list) for p in shopping_list: print(p) print("Your current balance:",salary) exit() else: print("invalid option")