def operation(self, op_id):
        """The operation details endpoint provides information on a single
        operation.

        `GET /operations/{id}
        <https://www.stellar.org/developers/horizon/reference/endpoints/operations-single.html>`_

        :param id op_id: The operation ID to get details on.
        :return: Details on a single operation.
        :rtype: dict
        """
        endpoint = '/operations/{op_id}'.format(op_id=op_id)
        return self.query(endpoint)