redis/redis-py · error · RedisError

Pattern ' ' has no handler registered

Error message

Pattern '{pattern}' has no handler registered

What it means

KeyspaceNotifications._validate_all_handlers (redis/keyspace_notifications.py:1728, standalone) raises RedisError when any pattern subscription (psubscribe) has a None handler. Same lifecycle as error 432 but for glob-pattern subscriptions. run_in_thread needs a callable per pattern to dispatch incoming messages.

Solutions

1. Pass a handler for every pattern subscription before run_in_thread.
2. Use get_message()/listen() if you intend to handle messages inline without per-pattern callbacks.
3. Audit all subscribe calls so every KeyspacePattern has a non-None handler.

Example fix

// before
notifications.subscribe(KeyspacePattern('user:*'))
notifications.run_in_thread()
// after
notifications.subscribe(KeyspacePattern('user:*'), handler=on_user_event)
notifications.run_in_thread(poll_timeout=0.1)

def all_patterns_have_handler(ksn) -> bool:
    return all(h is not None for _, h in ksn._pubsub.patterns.items())

When it happens

Trigger: notifications.subscribe(KeyspacePattern('user:*'), handler=None) then run_in_thread; subscribing a pattern for listen()/get_message() use and then switching to run_in_thread without a handler.

Common situations: Same as 432 for pattern-based subscriptions; forgetting handler on a KeyspacePattern subscribe.

Related errors

• Channel ' ' has no handler registered
• Pattern: ' ' has no handler registered
• Channel: ' ' has no handler registered
• Failed to subscribe to cluster nodes
• A non health check response was cleaned by execute_command

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/932bde4ea5e8f477. Report an issue: GitHub.

Appendix: source

Thrown at redis/keyspace_notifications.py:1728

        """
        while self.subscribed:
            notification = self.get_message(timeout=1.0)
            if notification is not None:
                yield notification

    @property
    def subscribed(self) -> bool:
        """Check if there are any active subscriptions and not closed."""
        return not self._closed and self._pubsub.subscribed

    def _validate_all_handlers(self) -> None:
        """Raise if any subscription in the underlying PubSub lacks a handler."""
        for channel, handler in self._pubsub.channels.items():
            if handler is None:
                raise RedisError(f"Channel '{channel}' has no handler registered")
        for pattern, handler in self._pubsub.patterns.items():
            if handler is None:
                raise RedisError(f"Pattern '{pattern}' has no handler registered")

    def close(self):
        """Close the pubsub connection and clean up resources."""
        self._closed = True
        try:
            self._pubsub.close()
        except Exception:
            pass


# =============================================================================
# Cluster-Aware Keyspace Notification Manager
# =============================================================================


class ClusterKeyspaceNotifications(AbstractKeyspaceNotifications):
    """
    Manages keyspace notification subscriptions across all nodes in a Redis Cluster.

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