code: def create_upload_url_async(success_path,
                              max_bytes_per_blob=None,
                              max_bytes_total=None,
                              **options):
    
    rpc = blobstore.create_rpc(**options)
    rpc = blobstore.create_upload_url_async(success_path,
                                            max_bytes_per_blob=max_bytes_per_blob,
                                            max_bytes_total=max_bytes_total,
                                            rpc=rpc)
    result = yield rpc
    raise tasklets.Return(result)
docs: Async version of create_upload_url().