code: def get_read_options(eventual, transaction_id):
      
      if transaction_id is None:
          if eventual:
              return datastore_pb2.ReadOptions(
                  read_consistency=datastore_pb2.ReadOptions.EVENTUAL
              )
          else:
              return datastore_pb2.ReadOptions()
      else:
          if eventual:
              raise ValueError("eventual must be False when in a transaction")
          else:
              return datastore_pb2.ReadOptions(transaction=transaction_id)
docs: Validate rules for read options, and assign to the request.
  
      Helper method for ``lookup()`` and ``run_query``.
  
      :type eventual: bool
      :param eventual: Flag indicating if ``EVENTUAL`` or ``STRONG``
                       consistency should be used.
  
      :type transaction_id: bytes
      :param transaction_id: A transaction identifier (may be null).
  
      :rtype: :class:`.datastore_pb2.ReadOptions`
      :returns: The read options corresponding to the inputs.
      :raises: :class:`ValueError` if ``eventual`` is ``True`` and the
               ``transaction_id`` is not ``None``.