python/cpython · error · ValueError

the socket must be non-blocking

Error message

the socket must be non-blocking

What it means

Error "the socket must be non-blocking" thrown in python/cpython.

Source

Thrown at Lib/asyncio/proactor_events.py:723

    async def sock_recvfrom(self, sock, bufsize):
        return await self._proactor.recvfrom(sock, bufsize)

    async def sock_recvfrom_into(self, sock, buf, nbytes=0):
        if not nbytes:
            nbytes = len(buf)

        return await self._proactor.recvfrom_into(sock, buf, nbytes)

    async def sock_sendall(self, sock, data):
        return await self._proactor.send(sock, data)

    async def sock_sendto(self, sock, data, address):
        return await self._proactor.sendto(sock, data, 0, address)

    async def sock_connect(self, sock, address):
        if self._debug and sock.gettimeout() != 0:
            raise ValueError("the socket must be non-blocking")
        return await self._proactor.connect(sock, address)

    async def sock_accept(self, sock):
        return await self._proactor.accept(sock)

    async def _sock_sendfile_native(self, sock, file, offset, count):
        try:
            fileno = file.fileno()
        except (AttributeError, io.UnsupportedOperation):
            raise exceptions.SendfileNotAvailableError("not a regular file")
        try:
            fsize = os.fstat(fileno).st_size
        except OSError:
            raise exceptions.SendfileNotAvailableError("not a regular file")
        blocksize = count if count else fsize
        if not blocksize:
            return 0  # empty file

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Call sock.setblocking(False) before registering the socket with the proactor event loop.

When it happens

Trigger: Raised when a blocking-mode socket is used with the proactor event loop.

Common situations: See trigger scenarios.

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/501ac7f2359f9fc8. Report an issue: GitHub.