Is there I can define expression for the placement of label in vector layer like when the scale is less than x label placement should be curved else it should be horizontal.

I am using Pal setting. I have following setting for the vector layer.

self.setCustomProperty('labeling/placement', '3')

Is there any way I can write expression for this like CASE $scale < 10000 THEN curved ELSE Horizontal END

placement is enum{Parallel, curved, horizontal} so its '3' in settings