code: def operation(self, op_id):
          
          endpoint = '/operations/{op_id}'.format(op_id=op_id)
          return self.query(endpoint)
docs: 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