python/cpython · error · ValueError

host and port was not specified and no sock specified

Error message

host and port was not specified and no sock specified

What it means

Raised by create_connection when neither host/port nor sock was provided. The method needs either an address to resolve-and-dial or an already-connected socket to adopt; with both absent there is nothing to connect, so it raises ValueError immediately.

Source

Thrown at Lib/asyncio/base_events.py:1192

                        raise exceptions[0]
                    elif exceptions:
                        # If they all have the same str(), raise one.
                        model = str(exceptions[0])
                        if all(str(exc) == model for exc in exceptions):
                            raise exceptions[0]
                        # Raise a combined exception so the user can see all
                        # the various error messages.
                        raise OSError('Multiple exceptions: {}'.format(
                            ', '.join(str(exc) for exc in exceptions)))
                    else:
                        # No exceptions were collected, raise a timeout error
                        raise TimeoutError('create_connection failed')
                finally:
                    exceptions = None

        else:
            if sock is None:
                raise ValueError(
                    'host and port was not specified and no sock specified')
            if sock.type != socket.SOCK_STREAM:
                # We allow AF_INET, AF_INET6, AF_UNIX as long as they
                # are SOCK_STREAM.
                # We support passing AF_UNIX sockets even though we have
                # a dedicated API for that: create_unix_connection.
                # Disallowing AF_UNIX in this method, breaks backwards
                # compatibility.
                raise ValueError(
                    f'A Stream Socket was expected, got {sock!r}')

        transport, protocol = await self._create_connection_transport(
            sock, protocol_factory, ssl, server_hostname,
            ssl_handshake_timeout=ssl_handshake_timeout,
            ssl_shutdown_timeout=ssl_shutdown_timeout)
        if self._debug:
            # Get the socket from the transport because SSL transport closes
            # the old socket and creates a new SSL socket

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Validate configuration before connecting: assert host and port are set (and port is an int).
2. Pass sock=... if your intent is to adopt an existing connected socket.
3. Fail fast at config load with a clear message instead of deep inside asyncio.

Example fix

// before
host = cfg.get('host')  # missing -> None
await loop.create_connection(proto, host, cfg.get('port'))

// after
host, port = cfg['host'], int(cfg['port'])
if not host or not port:
    raise ConfigError('host and port are required')
await loop.create_connection(proto, host, port)

if not host and sock is None:
    raise ConfigError('create_connection requires host/port or sock')

When it happens

Trigger: loop.create_connection(proto) or loop.create_connection(proto, None, None) — host and port default to None and no sock was passed. Common when host/port come from config and both resolve to None/empty.

Common situations: Config-driven clients where required host/port keys are missing and code passes the values through unchecked; parsers that strip values and yield None; test scaffolding that forgot to populate the target.

Related errors

• server_hostname is only meaningful with ssl
• host/port and sock can not be specified at the same time
• A Stream Socket was expected, got {sock!r}
• Semaphore initial value must be >= 0
• parties must be >= 1

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/37efea5fa995dcab. Report an issue: GitHub.