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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def auth_password(self, username, password, event=None, fallback=True):
 """ Authenticate to the server using a password. The username and password are sent over an encrypted link. If an ``event`` is passed in, this method will return immediately, and the event will be triggered once authentication succeeds or fails. On success, `is_authenticated` will return ``True``. On failure, you may use `get_exception` to get more detailed error information. Since 1.1, if no event is passed, this method will block until the authentication succeeds or fails. On failure, an exception is raised. Otherwise, the method simply returns. Since 1.5, if no event is passed and ``fallback`` is ``True`` (the default), if the server doesn't support plain password authentication but does support so-called "keyboard-interactive" mode, an attempt will be made to authenticate using this interactive mode. If it fails, the normal exception will be thrown as if the attempt had never been made. This is useful for some recent Gentoo and Debian distributions, which turn off plain password authentication in a misguided belief that interactive authentication is "more secure". (It's not.) If the server requires multi-step authentication (which is very rare), this method will return a list of auth types permissible for the next step. Otherwise, in the normal case, an empty list is returned. :param str username: the username to authenticate as :param basestring password: the password to authenticate with :param .threading.Event event: an event to trigger when the authentication attempt is complete (whether it was successful or not) :param bool fallback: ``True`` if an attempt at an automated "interactive" password auth should be made if the server doesn't support normal password auth :return: list of auth types permissible for the next stage of authentication (normally empty) :raises: `.BadAuthenticationType` -- if password authentication isn't allowed by the server for this user (and no event was passed in) :raises: `.AuthenticationException` -- if the authentication failed (and no event was passed in) :raises: `.SSHException` -- if there was a network error """

        if (not self.active) or (not self.initial_kex_done):
            # we should never try to send the password unless we're on a secure
            # link
            raise SSHException("No existing session")
        if event is None:
            my_event = threading.Event()
        else:
            my_event = event
        self.auth_handler = AuthHandler(self)
        self.auth_handler.auth_password(username, password, my_event)
        if event is not None:
            # caller wants to wait for event themselves
            return []
        try:
            return self.auth_handler.wait_for_response(my_event)
        except BadAuthenticationType as e:
            # if password auth isn't allowed, but keyboard-interactive *is*,
            # try to fudge it
            if not fallback or ("keyboard-interactive" not in e.allowed_types):
                raise
            try:

                def handler(title, instructions, fields):
                    if len(fields) > 1:
                        raise SSHException("Fallback authentication failed.")
                    if len(fields) == 0:
                        # for some reason, at least on os x, a 2nd request will
                        # be made with zero fields requested.  maybe it's just
                        # to try to fake out automated scripting of the exact
                        # type we're doing here.  *shrug* :)
                        return []
                    return [password]

                return self.auth_interactive(username, handler)
            except SSHException:
                # attempt failed; just raise the original exception
                raise e