Python 3.9 is now generally available.

google.appengine.api.images.vertical_flip_async

Asynchronously flips the image vertically.

image_data String of the source image data.
output_encoding A value from OUTPUT_ENCODING_TYPES.
quality A value between 1 and 100 to specify the quality of the encoding. This value is only used to control JPEG quality.
correct_orientation A value from ORIENTATION_CORRECTION_TYPE to indicate if orientation correction should be performed during the transformation.
rpc An optional UserRPC object.
transparent_substitution_rgb When transparent pixels are not supported in the destination image format, then transparent pixels will be substituted for the specified color, which must be in 32-bit RGB format.

A UserRPC object; call get_result() to complete the RPC and obtain the crop result.

Error All errors. See Image.ExecuteTransforms for more details.