Format filename of a :class:`Post` or :class:`StoryItem` according to ``filename-pattern`` parameter.

        .. versionadded:: 4.1

def format_filename(self, item: Union[Post, StoryItem], target: Optional[str] = None):
        """Format filename of a :class:`Post` or :class:`StoryItem` according to ``filename-pattern`` parameter.

        .. versionadded:: 4.1"""
        return _PostPathFormatter(item).format(self.filename_pattern, target=target)