def get_indicator(self, resource):
        """Return the modification time and size of a `Resource`."""
        path = resource.real_path
        # on dos, mtime does not change for a folder when files are added
        if os.name != 'posix' and os.path.isdir(path):
            return (os.path.getmtime(path),
                    len(os.listdir(path)),
                    os.path.getsize(path))
        return (os.path.getmtime(path),
                os.path.getsize(path))
Return the modification time and size of a `Resource`.