How to use the gphoto2.gp_file_get_data_and_size function in gphoto2

print('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)
    print('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)
    print(type(data), len(data))
    print(data[:10].tolist())
    image = Image.open(io.BytesIO(file_data))
    image.show()
    gp.check_result(gp.gp_camera_exit(camera))
    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)

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

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

def capture():
            path = gp.check_result(gp.gp_camera_capture(self._camera, gp.GP_CAPTURE_IMAGE, self._context))

            file = gp.check_result(gp.gp_camera_file_get(
                self._camera, path.folder, path.name,
                gp.GP_FILE_TYPE_NORMAL, self._context))

            data = gp.check_result(gp.gp_file_get_data_and_size(file))
            return bytes(data)