resonably decent hueristics for how much time to wait before
        updating progress.

def _get_timethresh_heuristics(self):
        """
        resonably decent hueristics for how much time to wait before
        updating progress.
        """
        if self.length > 1E5:
            time_thresh = 2.5
        elif self.length > 1E4:
            time_thresh = 2.0
        elif self.length > 1E3:
            time_thresh = 1.0
        else:
            time_thresh = 0.5
        return time_thresh