How to use the gphoto2.gp_camera_capture_preview function in gphoto2

def put_camera_capture_preview_mirror(camera, camera_config, camera_model):
    if camera_model == 'unknown':
        # find the capture size class config item
        # need to set this on my Canon 350d to get preview to work at all
        OK, capture_size_class = gp.gp_widget_get_child_by_name(
            camera_config, 'capturesizeclass')
        if OK >= gp.GP_OK:
            # set value
            value = capture_size_class.get_choice(2)
            capture_size_class.set_value(value)
            # set config
            camera.set_config(camera_config)
    else:
        # put camera into preview mode to raise mirror
        ret = gp.gp_camera_capture_preview(camera) # OK, camera_file
        #print(ret) # [0, ]

def _do_preview(self):
        # capture preview image
        OK, camera_file = gp.gp_camera_capture_preview(self.camera)
        if OK < gp.GP_OK:
            print('Failed to capture preview')
            self.running = False
            return
        self._send_file(camera_file)

def _do_preview(self):
        # capture preview image
        OK, camera_file = gp.gp_camera_capture_preview(self.camera)
        if OK < gp.GP_OK:
            print('Failed to capture preview')
            self.running = False
            return
        self._send_file(camera_file)

if 'raw' in value.lower():
            app.logger.debug('Cannot preview raw images')
            return 1
    # find the capture size class config item
    # need to set this on my Canon 350d to get preview to work at all
    OK, capture_size_class = gp.gp_widget_get_child_by_name(
        config, 'capturesizeclass')
    if OK >= gp.GP_OK:
        # set value
        value = gp.check_result(gp.gp_widget_get_choice(capture_size_class, 2))
        gp.check_result(gp.gp_widget_set_value(capture_size_class, value))
        # set config
        gp.check_result(gp.gp_camera_set_config(camera, config))
    # capture preview image (not saved to camera memory card)
    app.logger.debug('Capturing preview image')
    camera_file = gp.check_result(gp.gp_camera_capture_preview(camera))
    file_data = gp.check_result(gp.gp_file_get_data_and_size(camera_file))
    # display image
    data = memoryview(file_data)
    app.logger.debug(type(data), len(data))
    app.logger.debug(data[:10].tolist())
    fileName = os.path.join(PI_PREVIEW_DIR, PI_PREVIEW_FILE)
    if os.path.exists(fileName):
        os.remove(fileName)
    Image.open(io.BytesIO(file_data)).save(fileName, "JPEG")
    return 0

async def capture_preview(self):
        """ Capture preview image (doesn't engage curtain)
        """
        with (await self._lock):
            file = gp.check_result(gp.gp_camera_capture_preview(self._camera, self._context))
            data = gp.check_result(gp.gp_file_get_data_and_size(file))
            return bytes(data)