redis/redis-py · error · DataError

Passing a host requires passing a port, and vice versa

Error message

Passing a host requires passing a port, and vice versa

What it means

Raised as a DataError in the ClusterPubSub constructor when only one of host or port is provided (the other is None). The guard at cluster.py:3016-3018 uses any([host, port]) to detect the partial case. Both must be provided together or neither, because a node address requires both components to be meaningful.

Solutions

Provide both host and port together: client.pubsub(host='10.0.0.1', port=7000).
If you want the default node, pass neither: client.pubsub().
If you have a ClusterNode, pass node= instead: client.pubsub(node=my_node).

Example fix

// before
ps = client.pubsub(host='10.0.0.1')

// after
ps = client.pubsub(host='10.0.0.1', port=7000)

Defensive patterns

Strategy: validation

Validate before calling

# Validate host/port are both provided or both absent
if bool(host) != bool(port):
    raise ValueError('Provide both host and port, or neither')

Type guard

def host_port_pair_valid(host, port) -> bool:
    return (host is not None) == (port is not None)

Try / catch

null

Prevention

Always provide host and port together, or omit both to use the default node.
Extract host and port from the same config object to avoid partial values.

When it happens

Trigger: Calling client.pubsub(host='10.0.0.1') without port, or client.pubsub(port=7000) without host. Either triggers the DataError.

Common situations: Developer passes a host string but forgets the port, or extracts host and port from a config object where one value is missing.

Related errors

AI-assisted analysis of redis/redis-py@6a6b581b48 (2026-08-10). Data as JSON: /api/errors/627a83637c509908. Report an issue: GitHub.

Appendix: source

Thrown at redis/cluster.py:3018

        If host is passed without port, or vice versa, a DataError will be
        thrown.
        :type cluster: RedisCluster
        :type node: ClusterNode
        :type host: str
        :type port: int
        """
        if node is not None:
            # node is passed by the user
            self._raise_on_invalid_node(cluster, node, node.host, node.port)
            pubsub_node = node
        elif host is not None and port is not None:
            # host and port passed by the user
            node = cluster.get_node(host=host, port=port)
            self._raise_on_invalid_node(cluster, node, host, port)
            pubsub_node = node
        elif any([host, port]) is True:
            # only 'host' or 'port' passed
            raise DataError("Passing a host requires passing a port, and vice versa")
        else:
            # nothing passed by the user. set node to None
            pubsub_node = None

        self.node = pubsub_node

    def get_pubsub_node(self):
        """
        Get the node that is being used as the pubsub connection
        """
        return self.node

    def _raise_on_invalid_node(self, redis_cluster, node, host, port):
        """
        Raise a RedisClusterException if the node is None or doesn't exist in
        the cluster.
        """
        if node is None or redis_cluster.get_node(node_name=node.name) is None:

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