import bpy
import bpy.app

from mathutils import Vector
from mathutils import Quaternion

def calculateRotation(obj):
    up = Vector((0, 0, 1))
    diameter = obj.dimensions[0]
    previousLocation = Vector(tuple(obj.get("previousLocation", [0, 0, 0])))
    rotation = Quaternion(tuple(obj.get("previousRotation", [1, 0, 0, 0])))

    deltaLocation = obj.location - previousLocation
    distance = deltaLocation.length
    deltaLocation.normalize()
    axis = -deltaLocation.cross(up)
    angle = distance / diameter * 2

    rotation.rotate(Quaternion(axis, angle))

    obj["previousLocation"] = obj.location
    obj["previousRotation"] = rotation

    return rotation

bpy.app.driver_namespace["calculateRotation"] = calculateRotation