def _fromListeningDescriptor(cls, reactor, fd, addressFamily, factory):
        """
        Create a new L{Port} based on an existing listening I{SOCK_STREAM}
        socket.

        Arguments are the same as to L{Port.__init__}, except where noted.

        @param fd: An integer file descriptor associated with a listening
            socket.  The socket must be in non-blocking mode.  Any additional
            attributes desired, such as I{FD_CLOEXEC}, must also be set already.

        @param addressFamily: The address family (sometimes called I{domain}) of
            the existing socket.  For example, L{socket.AF_INET}.

        @return: A new instance of C{cls} wrapping the socket given by C{fd}.
        """
        port = socket.fromfd(fd, addressFamily, cls.socketType)
        interface = _getsockname(port)[0]
        self = cls(None, factory, None, interface, reactor)
        self._preexistingSocket = port
        return self

        Create a new L{Port} based on an existing listening I{SOCK_STREAM}
        socket.

        Arguments are the same as to L{Port.__init__}, except where noted.

        @param fd: An integer file descriptor associated with a listening
            socket.  The socket must be in non-blocking mode.  Any additional
            attributes desired, such as I{FD_CLOEXEC}, must also be set already.

        @param addressFamily: The address family (sometimes called I{domain}) of
            the existing socket.  For example, L{socket.AF_INET}.

        @return: A new instance of C{cls} wrapping the socket given by C{fd}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/tcp.py