Return sorted files in directory order

def sorted(self, wantdirs=False):
        """
        Return sorted files in directory order
        """

        def add_dir(dirs, d):
            dirs.add(d)
            logger.debug('add_dir added %s', d)
            if d != self.base:
                parent, _ = os.path.split(d)
                assert parent not in ('', '/')
                add_dir(dirs, parent)

        result = set(self.files)    # make a copy!
        if wantdirs:
            dirs = set()
            for f in result:
                add_dir(dirs, os.path.dirname(f))
            result |= dirs
        return [os.path.join(*path_tuple) for path_tuple in
                sorted(os.path.split(path) for path in result)]