Login and account system

Question

So here I wanted to make a system that registered a person's account. It remembers the person's email, account, first and last names, by writing to a file. You can login to that account by typing the email and password according to that email and then you would get a hello message, saying your first and last name that you used to register your account with.

data_text = []
first_names = []
last_names = []
emails = []
passwords = []

def user_choice():
    print('Hello user, create an account or login to an existing one.')
    choice = input('Insert "1" if you wish to create an account or "2" if you wish to login: ')
    print('\r')
    if choice == '1':
        create_account()
        user_choice()
    else:
        login_account()
        user_choice()

def register_info():
    with open('Login_Data.txt', 'r') as login_data:
        global data_text, first_names, last_names, emails, passwords
        data_text = login_data.readlines()
        for i in data_text:
            data_text[data_text.index(i)] = i.strip()
        emails = (data_text[2::4])

def create_account():
    with open('Login_Data.txt', 'a') as login_data:
        first_name = input('First name: ')
        last_name = input('Last name: ')
        email = input('Insert your Email adress: ')
        while email in emails:
            print('That email is already registered')
            email = input('Insert another Email adress: ')
        password = input('Create a password: ')
        passwordc = input('Confirm your password: ')
        info = [first_name, last_name, email, password]
        while passwordc != password:
            print('The passwords do not match.')
            passwordc = input('Reinsert your password: ')
        for i in info:
            login_data.write(i)
            login_data.write('\n')
    print('Nice! Your account was registered.')
    print('\r')
    register_info()

def login_account():
    register_info()
    with open('Login_Data.txt', 'r'):
        login_email = input('Email: ')
        while login_email not in emails:
            print('Invalid Email')
            login_email = input('Reinsert your Email: ')
        login_password = input('Password: ')
        while login_password != data_text[data_text.index(login_email) + 1]:
            print('Invalid password')
            login_password = input('Reinsert your password: ')
        print('Hello {} {}, welcome back!'.format(data_text[data_text.index(login_email) - 2], data_text[data_text.index(login_email) - 1]))
        print('\r')
user_choice()

Answer 1

• user_choice is your main loop, and so it would be better described as main. Whilst fairly undescriptive on what it does you can add a docstring to add information on what it performs.
• It is more idiomatic to use loops in Python rather than recursion. This is partly due to the recursion limit, and partially that the iterator pattern has a lot of support in Python.
• I've rarely seen '\r' in Python. I don't see why you would need it and so have just removed them.
• I like the way that you got a users email. The use of a while loop here is pretty clean.
• I would change the prompted text when getting an email as it's different to the rest of the prompts.
• I would DRY your do while loop. There's not really a point to having two different input prompts with the above suggestion.

• Recently I was creating an account using passwd and multiple times I kept messing up the first password entry. It was rather vexing as I knew I messed up and I just had to hope I pressed backspace the correct amount of times to fix my mess up. Unfortunately I wasn't skilled enough to fix my mistake.

  However with your solution I would have to quit out of your entire program, removing the data I have already to fix my mistake. You should instead get again the password and the confirmation.

• There is no point in opening login_data until the user input has been confirmed to be correct. You should try to keep with statements as small as necessary.
• I would prefer to build a dictionary or an abstract datatype for the user information.
• You can remove one of your login_data.writes by passing i + '\n'.
• "Login_Data.txt" seems ok, but it's not great. You can use JSON via import json and make a much easier and standard file type to work with.

• Your interactions with your globals seem really poor. If you want a global, than I suggest you only have one. This is easy when using dictionaries.

  I would also suggest changing your code to have no globals.

• I would change login_account to align with the above, changed do-while loops, no globals and using JSON.
• Since we are using JSON we can easily change the format to display the first and last name easier.
• Your solution is in no way safe, it's prone to over the shoulder attacks by not using getpass and you're storing passwords in plain-text. This is not safe. Do not use this for anything more than a toy project that will only ever have you entering a password unique to this toy.

import json


def main():
    """Create an account or log in."""
    while True:
        print('Hello user, create an account or login to an existing one.')
        choice = input('Insert "1" if you wish to create an account or "2" if you wish to login: ')
        print()
        if choice == '1':
            create_account()
        else:
            login_account()


def input_user_email(emails):
    """Get an unowned email."""
    while True:
        email = input('Email: ')
        if email not in emails:
            return email
        print('That email is already registered.')


def input_user_password():
    """Get a user's email."""
    while True:
        password = input('Password: ')
        confirmation = input('Confirm password: ')
        if password == confirmation:
            return password
        print('The passwords do not match.')


def get_user_information(emails):
    """Get a user's information."""
    return {
        'first_name': input('First Name: '),
        'last_name': input('Last Name: '),
        'email': input_user_email(emails),
        'password': input_user_password(),
    }


def create_account():
    """Create user account."""
    with open('login_data.json', 'w+') as f:
        users = json.load(f)
        emails = {user['email'] for user in users}
        user = get_user_information(emails)
        users.append(user)
        json.dump(users, f)
    print('Nice! Your account was registered.\n')


def login_account():
    """Log into a user account."""
    with open('login_data.json') as f:
        users = json.load(f)
    by_email = {user['email']: user for user in users}

    while True:
        email = input('Email: ')
        if email in by_email:
            user = by_email[email]
            break
        print('Invalid Email')

    while True:
        password = input('Password: ')
        if password == user['password']:
            break
        print('Invalid password')

    print('Hello {0.first_name} {0.last_name}, welcome back!\n'.format(user))


if __name__ == '__main__':
    main()

Answer 2

_{Conversion of a comment to an answer.}

Definitely avoid the recursion in user_choice. It will run out of stack if you keep exercising it for long enough. A simple while True: around the rest of the function body should fix it (obviously take out the calls where it calls itself).
- tripleee