code: def fetch_data_async(blob, start_index, end_index, **options):
    
    if isinstance(blob, BlobInfo):
      blob = blob.key()
    rpc = blobstore.create_rpc(**options)
    rpc = blobstore.fetch_data_async(blob, start_index, end_index, rpc=rpc)
    result = yield rpc
    raise tasklets.Return(result)
docs: Async version of fetch_data().