def __init__(self, reactor, executable, args, environment, path, proto,
                 uid=None, gid=None, usePTY=None):
        """
        Spawn an operating-system process.

        This is where the hard work of disconnecting all currently open
        files / forking / executing the new process happens.  (This is
        executed automatically when a Process is instantiated.)

        This will also run the subprocess as a given user ID and group ID, if
        specified.  (Implementation Note: this doesn't support all the arcane
        nuances of setXXuid on UNIX: it will assume that either your effective
        or real UID is 0.)
        """
        if pty is None and not isinstance(usePTY, (tuple, list)):
            # no pty module and we didn't get a pty to use
            raise NotImplementedError(
                "cannot use PTYProcess on platforms without the pty module.")
        abstract.FileDescriptor.__init__(self, reactor)
        _BaseProcess.__init__(self, proto)

        if isinstance(usePTY, (tuple, list)):
            masterfd, slavefd, _ = usePTY
        else:
            masterfd, slavefd = pty.openpty()

        try:
            self._fork(path, uid, gid, executable, args, environment,
                       masterfd=masterfd, slavefd=slavefd)
        except:
            if not isinstance(usePTY, (tuple, list)):
                os.close(masterfd)
                os.close(slavefd)
            raise

        # we are now in parent process:
        os.close(slavefd)
        fdesc.setNonBlocking(masterfd)
        self.fd = masterfd
        self.startReading()
        self.connected = 1
        self.status = -1
        try:
            self.proto.makeConnection(self)
        except:
            log.err()
        registerReapProcessHandler(self.pid, self)

        Spawn an operating-system process.

        This is where the hard work of disconnecting all currently open
        files / forking / executing the new process happens.  (This is
        executed automatically when a Process is instantiated.)

        This will also run the subprocess as a given user ID and group ID, if
        specified.  (Implementation Note: this doesn't support all the arcane
        nuances of setXXuid on UNIX: it will assume that either your effective
        or real UID is 0.)
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/process.py