创建登录系统

Question

I am trying to create a login system. I could make the system without implementing class and just functions. I would like to make each steps into specific methods without writing all into one function.

My question is how to revert back into login asking username and password if the character length is > 5 or wrong password.

If the username and password not in the list how do i revert it back or do i need to code again?

    class LoginSystem:

        def __init__(self):
            self.user_id = input("Please enter your user id: ")
            self.user_password = input("Please enter your password: ")

        def login(self):
            username = self.user_id
            password = self.user_password
            if len(username) <= 5 and len(password) <= 5:
                print("Logging In")
            else:
                print("Error! Max Length is 5 chars.") #return back to 
                login system

        def check_system(self):
            registered_user = {
             "test@gmail.com": "test"
            }
            if self.user_id in registered_user:
                print("Successful")
            else:
                new_user = input("Id not found! Are you are new user?\n [Y]es or [N]o\n")
                new_user = new_user.lower()
                if new_user == "Y":
                   return back to login system
                elif new_user == "N": #how to return back to main login system
                   new_username = input("Please enter your user id: ")
                   new_userpassword = input("Please enter your password: ")
                else:
                   return #back to login system

Answer 1

Your LoginSystem treats the wrong data as its instance attributes. The set of registered users is constant across method calls; the login method itself should be prompting for the user id and password.

class LoginSystem:

    def __init__(self):
        self.users = {"test@gmail.com": "test"}

    def login(self):
        while True:
            username = input("Please enter your user id: ")
            password = input("Please enter your password: ")
            if len(username) <= 5 and len(password) <= 5 and self.check_system(username, password):
                print("Logging In")
                break
            else:
                # TODO Disallow infinite retries to get it right
                print("Error! Max Length is 5 chars.")

    def check_system(self, name, password):
        try:
            expected_password = self.registered_user[name]
        except KeyError:
            # Or try to add a new user to the system here
            return False

        if password != expected_password:
            return False

        return True

A separate method can be added to add a new user to the system where necessary.