darf.py

@persistent
def sv_update_handler(scene):
    """
    Update sverchok node groups on frame change events.
    """
    if not has_frame_changed(scene):
        return
    
    for ng in sverchok_trees():
        try:
            # print('sv_update_handler')
            ng.process_ani()
        except Exception as e:
            print('Failed to update:', str(e)) #name,

    #  something like this
    if sverchok.settings.dont_loop_animation:
        if scene.last_frame == scene.frame_current:
            bpy.ops.screen.animation_cancel()  # restore_frame=True)
            return

    scene.update()