Render current frame with arnold to jpeg and return path

render_frame_arnold.py

    def render_current_frame_ai(self):
        import tempfile, random
        from arnold import *
        d = tempfile.gettempdir()
        fi = join(d,'preview_image_%s' % random.randrange(10000, 99999))
        fa = join(d,'preview_image_%s' % random.randrange(10000, 99999)) + '.ass'

        rg = PyNode('defaultRenderGlobals')
        dr = PyNode('defaultResolution')
        ar = PyNode('defaultArnoldDriver')
        # backup
        old_format = ar.aiTranslator.get()
        oldW, oldH =dr.width.get(), dr.height.get()
        old_path = rg.imageFilePrefix.get()
        res = self.persp_res_cbb.currentIndex()
        dr.width.set(v.res_repsp[res][0])
        dr.height.set(v.res_repsp[res][1])
        # set values
        ar.aiTranslator.set('jpeg')
        rg.imageFilePrefix.set(fi)
        # render ass
        cam = ui.PyUI(playblast(activeEditor=True)).getCamera()
        file = cmds.arnoldExportAss(f=fa, startFrame=currentTime(), endFrame=currentTime(),
                                 mask=255, lightLinks=1, frameStep=1.0, shadowLinks=1,
                                 cam=cam)
        # restore
        ar.aiTranslator.set(old_format)
        rg.imageFilePrefix.set(old_path)
        dr.width.set(oldW)
        dr.height.set(oldH)
        # render jpg
        AiBegin()
        AiLoadPlugins(os.environ['ARNOLD_PLUGIN_PATH'])
        AiASSLoad (file[0], AI_NODE_ALL)
        AiRender()
        AiEnd()
        os.remove(file[0])
        # os.startfile(fi+'.jpeg')
        return fi+'.jpeg'