'Lookup some entities by key
see https://cloud.google.com/datastore/docs/apis/v1beta2/datasets/lookup
:param keys: the keys to lookup
:param read_consistency: the read consistency to use. default, strong or eventual.
Cannot be used with a transaction.
:param transaction: the transaction to use, if any.
:return: the response body of the lookup request.'

def lookup(self, keys, read_consistency=None, transaction=None):

    body = {'keys': keys}
    if read_consistency:
        body['readConsistency'] = read_consistency
    if transaction:
        body['transaction'] = transaction
    return self.connection.datasets().lookup(datasetId=self.dataset_id, body=body).execute()
