class User:
    def __init__(self, login, password):
        self._login = login
        self._password = password
    def login(self, new_login=None):
        if new_login != None:
            self._login = new_login
        else:
            return self._login
    def password(self, new_password):
        self._password = new_password
    def info(self):
        return self._login
    def __str__(self):
        return self._login
class Teacher(User):
    def __init__(self, login, password, name, surname, subject):
        self._login = login
        self._password = password
        self._name = name
        self._surname = surname
        self._subject = subject
    def name(self, new_name=None):
        if new_name != None:
            self._name = new_name
        else:
            return self._name
    def surname(self, new_surname=None):
        if new_surname != None:
            self._surname = new_surname
        else:
            return self._surname
    def subject(self, new_subject=None):
        if new_subject != None:
            self._subject = new_subject
        else:
            return self._subject
    def info(self):
        return '{}: {} {} {}'.format(self._subject, self._surname, self._login, self._name)
    def __str__(self):
        return '{}: {} {} {}'.format(self._subject, self._surname, self._login, self._name)