How to use the taguette.web.base._f function in taguette

login = self.get_body_argument('login')
            password1 = self.get_body_argument('password1')
            password2 = self.get_body_argument('password2')
            login = validate.user_login(login)
            validate.user_password(password1)
            email = self.get_body_argument('email', '')
            if email:
                validate.user_email(email)
            if password1 != password2:
                raise validate.InvalidFormat(_f("Passwords do not match"))
            if self.db.query(database.User).get(login) is not None:
                raise validate.InvalidFormat(_f("User name is taken"))
            if (email and
                    self.db.query(database.User)
                    .filter(database.User.email == email).count() > 0):
                raise validate.InvalidFormat(_f("Email address is already "
                                                "used"))
            user = database.User(login=login)
            user.set_password(password1)
            if email:
                user.email = email
            self.db.add(user)
            self.db.commit()
            logger.info("User registered: %r", login)
            self.set_secure_cookie('user', login)
            return self.redirect(self.reverse_url('index'))
        except validate.InvalidFormat as e:
            logger.info("Error validating Register: %r", e)
            return self.render('login.html', register=True,
                               register_error=self.gettext(e.message))

def decode_reset_token(self, reset_token):
        reset_token_clear = self.get_secure_cookie(
            'reset_token',
            reset_token,
            min_version=2,
            max_age_days=1,
        )
        if reset_token_clear is None:
            raise HTTPError(403, _f("Invalid token"))
        ts, login, email = reset_token_clear.decode('utf-8').split('|', 2)
        user = self.db.query(database.User).get(login)
        if not user or user.email != email:
            raise HTTPError(403, _f("No user associated with that token"))
        if user.password_set_date >= datetime.utcfromtimestamp(int(ts)):
            # Password has been changed after the reset token was created
            raise HTTPError(403, _f("Password has already been changed"))
        return user

def decode_reset_token(self, reset_token):
        reset_token_clear = self.get_secure_cookie(
            'reset_token',
            reset_token,
            min_version=2,
            max_age_days=1,
        )
        if reset_token_clear is None:
            raise HTTPError(403, _f("Invalid token"))
        ts, login, email = reset_token_clear.decode('utf-8').split('|', 2)
        user = self.db.query(database.User).get(login)
        if not user or user.email != email:
            raise HTTPError(403, _f("No user associated with that token"))
        if user.password_set_date >= datetime.utcfromtimestamp(int(ts)):
            # Password has been changed after the reset token was created
            raise HTTPError(403, _f("Password has already been changed"))
        return user

def tag_path(path):
    if not path:
        raise InvalidFormat(_f("Tag path cannot be empty"))
    if len(path) > 200:
        raise InvalidFormat(_f("Tag path is too long"))

def project_description(description):
    if len(description) > 102400:
        raise InvalidFormat(_f("Project description is too long"))

def document_description(description):
    if len(description) > 102400:
        raise InvalidFormat(_f("Document description is too long"))

def user_login(login):
    if not login:
        raise InvalidFormat(_f("User login cannot be empty"))
    if len(login) > 20:
        raise InvalidFormat(_f("User login is too long"))
    login = login.lower()
    if any(c not in ALLOWED_LOGIN_CHARACTERS
           for c in login):
        raise InvalidFormat(_f("User login contains forbidden characters"))
    return login