def send_static_file(self, filename: str) -> Response:
        """The view function used to serve files from
        :attr:`static_folder`. A route is automatically registered for
        this view at :attr:`static_url_path` if :attr:`static_folder` is
        set.

        Note this is a duplicate of the same method in the Flask
        class.

        .. versionadded:: 0.5

        """
        if not self.has_static_folder:
            raise RuntimeError("'static_folder' must be set to serve static_files.")

        # send_file only knows to call get_send_file_max_age on the app,
        # call it here so it works for blueprints too.
        max_age = self.get_send_file_max_age(filename)
        return send_from_directory(
            t.cast(str, self.static_folder), filename, max_age=max_age
        )
The view function used to serve files from
        :attr:`static_folder`. A route is automatically registered for
        this view at :attr:`static_url_path` if :attr:`static_folder` is
        set.

        Note this is a duplicate of the same method in the Flask
        class.

        .. versionadded:: 0.5

        
src/flask/blueprints.py