如何打开Python pickle文件、追加、保存和关闭它？

这是我的密码：

 import pickle


 class User:
     def __init__(self, username, password):
         self.username = username
         self.password = password

     def set_password(self):
         self.password = input("Enter NEW password > ")

     def __get_password(self):
         return self.password

     def __get_username(self):
         return self.username

     def change_password(self):
         my_password = input("Enter your CURRENT password > ")
         if my_password == User.__get_password(self):
             self.set_password()
         else:
             print("Please try again")

     def display_details(self):
         print()
         print("Username and password")
         print("---------------------")
         print("username is: ", User.__get_username(self))
         print("password is: ", User.__get_password(self))
         print()

     def __repr__(self):
         return f'username: {self.username}'


 users = [User("MichaelPalin", "P4rr0t"), User("EricIdle", "M0nty"), User("TerryJones", "Pyth0n")]

 try:
     foo = pickle.load(open("users.pickle", "rb"))
 except (OSError, IOError) as f:
     foo = 3
     pickle.dump(foo, open("users.pickle", "wb"))

 # with open('users.pickle', 'wb') as f:
 #     pickle.dump(users, f)


 def find_user(name):
     for user in users:
         if user.username == name:
             return user


 def add_user():
     user = input("Enter NEW user > ")
     password = input(f"Enter password for {user} > ")
     users.append(User(user, password))


 def delete_user():
     delete_user = input("Enter the user you wish to remove > ")
     user = find_user(delete_user)
     if user:
         users.remove(user)
         print('done')
     else:
         print(f'user {delete_user} not found')


 def change_password():
     my_password = input("Enter your CURRENT password > ")
     change_password()


 def display_users():
     for user in users:
         print(user)


 def invalid_entry():  # Response for invalid entries to menu.
     print("Invalid entry, please try again")
     print()


 def menu():  # Display menu, prompt for and accept keyboard choice
     print("Please select one of the following:")
     print()
     print("Enter a if you want to add a new user")
     print("Enter d if you want to delete a user")
     print("Enter f if you want to find a user")
     print("Enter c if you want to change your password")
     print("Enter u if you want to display a list of users")
     print("Enter q if you want to Quit")
     choice = input("")
     return choice


 while True:
     menu_choice = menu()
     if menu_choice.lower() == "a":
         add_user()
     elif menu_choice.lower() == "d":
         delete_user()
     elif menu_choice.lower() == "f":
         find_user()
     elif menu_choice.lower() == "c":
         change_password()
     elif menu_choice.lower() == 'u':
         display_users()
     elif menu_choice.lower() == "q":
         print("Goodbye")
         with open('users.pickle', 'wb') as f:
             pickle.dump(users, f)
             quit()
     else:
         invalid_entry()

但它不能正常工作，因为每次程序运行时都会覆盖pickle文件。我猜罪魁祸首是

用户

行，但如果是这样的话，我不知道如何解决问题。我尝试将整行移动到

try

部分的底部，与

pickle.dump

行对齐，但这只是抛出了一个错误：

NameError:未定义名称“用户”

有人能帮我吗？我已经试着这样做了大约两周了，现在我越来越沮丧了。我在网上看过很多相关的教程，现在看到的很多链接都是紫色的，但我似乎不知道如何编写代码来创建正确的逻辑流

我认为逻辑应该是：

1） 文件是否存在？
如果Y-什么也不做
如果N-使用示例数据创建它

2） 用户是否要创建新登录？
如果是Y-将登录名附加到文件

---

如果N-do nothing

我发现的问题是，您实际上没有在这些行中使用加载的pickle数据：

users = [User("MichaelPalin", "P4rr0t"), User("EricIdle", "M0nty"), User("TerryJones", "Pyth0n")]

 try:
     foo = pickle.load(open("users.pickle", "rb"))
 except (OSError, IOError) as f:
     foo = 3
     pickle.dump(foo, open("users.pickle", "wb"))

您将文件加载到

foo

中，但从不使用它，而且您的异常也没有多大意义，请尝试将该块更改为以下内容：

 try:
     users = pickle.load(open("users.pickle", "rb"))
 except (OSError, IOError) as f:
     users = [User("MichaelPalin", "P4rr0t"), User("EricIdle", "M0nty"), User("TerryJones", "Pyth0n")]
     pickle.dump(foo, open("users.pickle", "wb"))

现在，您将尝试加载预先制作的文件，如果失败，请生成默认文件，然后尝试以下代码：

try:
    users = pickle.load(open("users.pickle", "rb"))
except (OSError, IOError) as f:
    foo = 3
    print("except")
    pickle.dump(users, open("users.pickle", "wb"))

另外，退出（）outside with:

with open('users.pickle', 'wb') as f:
    pickle.dump(users, f)
quit()

---

pickle是一个倾斜的结构，你可以在不修改头部的情况下附加一些东西的想法是不正确的。@tripleee-恐怕我不知道你的意思。我试着在谷歌上搜索“pickle是一个斜结构”，但我还是不知道。他的意思是pickle不是一个你可以附加的文本文件，它是一个你必须重写的二进制对象，这就是你想要的do@Nullman-我明白了，谢谢。谢谢！！！终于破解了！哈利路亚！！事实上，我在尝试将

用户

行放入该块时已经走得不远了，但我做得不对。再次感谢。在回答问题时，试着解释一下为什么你的解决方案回答了原始海报的问题。这将帮助其他用户快速确定您的答案是否也适用于他们的问题。