def get_relative_log(self, output_file):
        """
        Try to get the relative path of log.txt
        :param output_file: output file: log.html
        :return: ./log.txt or ""
        """
        try:
            html_dir = os.path.dirname(output_file)
            if self.export_dir:
                # When exporting reports, the log directory will be named log/ (DEFAULT_LOG_DIR),
                # so the relative path of log.txt is log/log.txt
                return os.path.join(DEFAULT_LOG_DIR, os.path.basename(self.logfile))
            return os.path.relpath(os.path.join(self.log_root, self.logfile), html_dir)
        except:
            LOGGING.error(traceback.format_exc())
            return ""

        Try to get the relative path of log.txt
        :param output_file: output file: log.html
        :return: ./log.txt or ""
        
airtest/report/report.py