def speed(self) -> Optional[float]:
        """Optional[float]: Get the estimated speed in steps per second."""
        if self.start_time is None:
            return None
        with self._lock:
            progress = self._progress
            if not progress:
                return None
            total_time = progress[-1].timestamp - progress[0].timestamp
            if total_time == 0:
                return None
            iter_progress = iter(progress)
            next(iter_progress)
            total_completed = sum(sample.completed for sample in iter_progress)
            speed = total_completed / total_time
            return speed
Optional[float]: Get the estimated speed in steps per second.
rich/progress.py