def get_boottime(self):
        return self._last_tick - self._start_tick
@param target: total number of steps expected
dataset/ETHPy150Open kivy/kivy/kivy/clock.py/ClockBase.get_boottime--crossover with--dataset/ETHPy150Open hycis/Mozi/mozi/utils/progbar.py/Progbar.__init__