def childDataReceived(self, childFD, data):
        """
        Override and disable the dispatch provided by the base class to ensure
        that it is really this method which is being called, and the transport
        is not going directly to L{outReceived} or L{errReceived}.
        """
        if childFD == 1:
            self.data += data
        elif childFD == 2:
            self.err += data

        Override and disable the dispatch provided by the base class to ensure
        that it is really this method which is being called, and the transport
        is not going directly to L{outReceived} or L{errReceived}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_process.py