redis/redis-py · error · ValueError

Cannot enable maintenance notifications for connection…

Error message

Cannot enable maintenance notifications for connection object that doesn't have a host attribute.

What it means

ValueError from Connection._enable_maintenance_notifications (redis/asyncio/connection.py:393) when the connection object has no 'host' attribute (host is None). The MAINT_NOTIFICATIONS command needs an endpoint type derived from the host; a connection without one (some internal/specialized connection types) cannot enable the feature. This is effectively an internal precondition failure.

Solutions

Provide a host attribute on the connection before enabling maintenance notifications
Use the standard connection classes that always set host
Disable maintenance notifications for connections that have no host

Defensive patterns

Strategy: validation

Validate before calling

if getattr(conn, 'host', None) is None:
    raise ValueError('connection has no host; cannot enable maintenance notifications')

Prevention

Only enable maintenance notifications on connections that carry a host
Use the standard connection classes in production paths

When it happens

Trigger: Enabling maintenance notifications on a connection type that does not carry a host attribute (e.g. a wrapped or mock connection); pool handing the enable call to a connection subclass missing host.

Common situations: Testing with mock connections; custom connection subclasses used in multidb/failover paths.

Related errors

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/55c04028f08ba389. Report an issue: GitHub.

Appendix: source

Thrown at redis/asyncio/connection.py:401

            and self.maint_notifications_config
            and self.maint_notifications_config.enabled
            and self._maint_notifications_connection_handler
            and host is not None
        ):
            await self._enable_maintenance_notifications(
                maint_notifications_config=self.maint_notifications_config,
                check_health=check_health,
            )

    async def _enable_maintenance_notifications(
        self,
        maint_notifications_config: MaintNotificationsConfig,
        check_health: bool = True,
    ) -> None:
        try:
            host = getattr(self, "host", None)
            if host is None:
                raise ValueError(
                    "Cannot enable maintenance notifications for connection"
                    " object that doesn't have a host attribute."
                )

            endpoint_type = maint_notifications_config.get_endpoint_type(host, self)
            await self.send_command(
                "CLIENT",
                "MAINT_NOTIFICATIONS",
                "ON",
                "moving-endpoint-type",
                endpoint_type.value,
                check_health=check_health,
            )
            response = await self.read_response()
            if not response or str_if_bytes(response) != "OK":
                raise ResponseError(
                    "The server doesn't support maintenance notifications"
                )

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