def log_random_sleep(self, minimum=3.0, scale=1.0, hints=None):
        """wrap random sleep.

        - log it for debug purpose only
        """
        hints = '{} slept'.format(hints) if hints else 'slept'
        st = time.time()
        helper.random_sleep(minimum, scale)
        log.debug('{} {} {}s'.format(
            self.symbols.get('sleep', ''), hints, self.color_log(time.time() - st)))