def describe_databases(self, db_instance_identifier=None):
        if db_instance_identifier:
            if db_instance_identifier in self.databases:
                return [self.databases[db_instance_identifier]]
            else:
                raise DBInstanceNotFoundError(db_instance_identifier)
        return self.databases.values()
dataset/ETHPy150Open spulec/moto/moto/rds/models.py/RDSBackend.describe_databases/original