Pickle file not being written to properly

Question

Here is my code:

 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()

...but it's clearly not working properly, as though I can add a new user, once I restart my app, the new user is gone.

The first thing I want to do is read the pickle file in, right? But how can I read it in if it doesn't yet exist? So in that case that surely means I need to write it at first. But when I do that, I'm over-writing the existing file !

I tried using pickle.load as mentioned here , but it's just coming back "TypeError: load() takes exactly 1 positional argument (2 given)".

Any help please?

Edit: I made a couple of changes. The problem of over-writing the file is clearly not solved yet though.

Answer 1

I am not sure if I have got the answer but there was a little indentation issue (in my opinion) .. formatted code is as below.

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")]


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


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


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


def add_user():
    user = input("Enter NEW user > ")
    password = input(f"Enter password for {user} > ")
    users.append(User(user, password))
    with open('users.pickle', 'wb') as f:
        pickle.dump(users, f)


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 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 1 if you want to add a new user")
    print("Enter 2 if you want to delete a user")
    print("Enter 3 if you want to change your password")
    print("Enter u if you want to display a list of users")
    print("Enter 4 if you want to Quit")
    choice = input("")
    return choice


while True:
    menu_choice = menu()
    if menu_choice == "1":
        add_user()
    elif menu_choice == "2":
        delete_user()
    elif menu_choice == "3":
        change_password()
    elif menu_choice.lower() == 'u':
        display_users()
    elif menu_choice == "4":
        print("Goodbye")
        quit()
    else:
        invalid_entry()

This gives me the expected output as below.

Please select one of the following:

Enter 1 if you want to add a new user
Enter 2 if you want to delete a user
Enter 3 if you want to change your password
Enter u if you want to display a list of users
Enter 4 if you want to Quit
1
Enter NEW user > TestUser
Enter password for TestUser > TestPassword
Please select one of the following:

Enter 1 if you want to add a new user
Enter 2 if you want to delete a user
Enter 3 if you want to change your password
Enter u if you want to display a list of users
Enter 4 if you want to Quit
u
username: MichaelPalin
username: EricIdle
username: TerryJones
username: TestUser
Please select one of the following:

Enter 1 if you want to add a new user
Enter 2 if you want to delete a user
Enter 3 if you want to change your password
Enter u if you want to display a list of users
Enter 4 if you want to Quit
4
Goodbye

To load the updated "users.pickle" file, I typed the below.

with open("/FullPathToPickleFile/users.pickle","rb") as Handle:
    pickle.load(Handle)

and this gave me the following output.

[username: MichaelPalin, username: EricIdle, username: TerryJones, username: TestUser]

As you can see the TestUser has been added. if you wanted to see the updated users as in the pickled file, I would have put the above mentioned two lines of code inside the display_users() as below.

def display_users():
    with open("/FullPathToPickleFile/users.pickle","rb") as Handle:
        print(pickle.load(Handle))

With these change, you should be able to update the users and see the updated list.

Is this what you wanted?