def pump(self):
        """Move data back and forth.

        Returns whether any data was moved.
        """
        self.clientIO.seek(0)
        self.serverIO.seek(0)
        cData = self.clientIO.read()
        sData = self.serverIO.read()
        self.clientIO.seek(0)
        self.serverIO.seek(0)
        self.clientIO.truncate()
        self.serverIO.truncate()
        for byte in cData:
            self.server.dataReceived(byte)
        for byte in sData:
            self.client.dataReceived(byte)
        if cData or sData:
            return 1
        else:
            return 0
Move data back and forth.

        Returns whether any data was moved.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/testutils.py