code: def get_multi_instances_by_id(self, instance_ids):
          
          result = []
  
          for reservation in self.all_reservations():
              for instance in reservation.instances:
                  if instance.id in instance_ids:
                      result.append(instance)
  
          # TODO: Trim error message down to specific invalid id.
          if instance_ids and len(instance_ids) > len(result):
              raise InvalidInstanceIdError(instance_ids)
  
          return result
docs: :param instance_ids: A string list with instance ids
          :return: A list with instance objects