'Constructor.
This class is constructed in stages (one when an RPC is sent and another
when an rpc is completed) and should not be constructed directly!!
Use Query.run_async().get_result() to create a Batch or Query.run()
to use a batcher.
This constructor does not perform verification.
Args:
batch_shared: Data shared between batches for a a single query run.
start_cursor: Optional cursor pointing before this batch.'

@datastore_rpc._positional(2)
def __init__(self, batch_shared, start_cursor=Cursor()):

    self._batch_shared = batch_shared
    self.__start_cursor = start_cursor
