def __init__(self, system, openFlags, fileMode):
        """
        @param system: An L{_IInputOutputSystem} provider to use to perform I/O.

        @param openFlags: Any flags to apply when opening the tunnel device.
            See C{os.O_*}.

        @type openFlags: L{int}

        @param fileMode: ignored
        """
        self.system = system

        # Drop fileMode on the floor - evidence and logic suggest it is
        # irrelevant with respect to /dev/net/tun
        self.openFlags = openFlags
        self.tunnelMode = None
        self.requestedName = None
        self.name = None
        self.readBuffer = deque()
        self.writeBuffer = deque()
        self.pendingSignals = deque()

        @param system: An L{_IInputOutputSystem} provider to use to perform I/O.

        @param openFlags: Any flags to apply when opening the tunnel device.
            See C{os.O_*}.

        @type openFlags: L{int}

        @param fileMode: ignored
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/pair/testing.py