Changing Texture Slot and Clone Slot Using Python

How do you change which index is used for these:

bpy.context.object.active_material.paint_active_slot = index number
and
bpy.context.object.active_material.paint_active_slot = index number

Seem to be read only or I am misusing them by just assigning them a new index. Thanks in advance.

I can’t find the answer anywhere in the documentation.