python/cpython · error · ValueError

Neither host/port nor sock were specified

Error message

Neither host/port nor sock were specified

What it means

Raised by create_server() when neither host/port nor sock was provided — the method has no endpoint to listen on. create_server requires at least one binding source: an address pair or a pre-bound socket.

Source

Thrown at Lib/asyncio/base_events.py:1666

                            sockets.pop()
                            sock.close()
                            if self._debug:
                                logger.warning(msg)
                            continue
                        raise OSError(err.errno, msg) from None

                if not sockets:
                    raise OSError('could not bind on any address out of %r'
                                  % ([info[4] for info in infos],))

                completed = True
            finally:
                if not completed:
                    for sock in sockets:
                        sock.close()
        else:
            if sock is None:
                raise ValueError('Neither host/port nor sock were specified')
            if sock.type != socket.SOCK_STREAM:
                raise ValueError(f'A Stream Socket was expected, got {sock!r}')
            sockets = [sock]

        for sock in sockets:
            sock.setblocking(False)

        server = Server(self, sockets, protocol_factory,
                        ssl, backlog, ssl_handshake_timeout,
                        ssl_shutdown_timeout)
        if start_serving:
            server._start_serving()
            # Skip one loop iteration so that all 'loop.add_reader'
            # go through.
            await tasks.sleep(0)

        if self._debug:
            logger.info("%r is serving", server)

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Pass host and port, e.g. create_server(factory, '127.0.0.1', 8080)
2. Or pass a pre-bound socket via sock=listener
3. Use create_server(factory, None, port) to bind all interfaces on a port

Example fix

# before
server = await loop.create_server(factory)

# after
server = await loop.create_server(factory, '127.0.0.1', 8080)

if sock is None and host is None and port is None:
    raise ValueError('server endpoint required: pass (host, port) or sock=')

When it happens

Trigger: loop.create_server(factory) with all of host, port, sock defaulting to None; or passing host=None, port=None explicitly while forgetting sock.

Common situations: Building a server from config where host/port keys are missing/None and no socket fallback is wired; refactoring away the sock= parameter and leaving nothing behind.

Related errors

• ssl argument must be an SSLContext or None
• Node can't be used without a value attribute.
• host and port was not specified and no sock specified
• socket modifier keyword arguments can not be used when sock
• getaddrinfo({host!r}) returned empty list

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/efae08e4588d3c67. Report an issue: GitHub.