def dataReceived(self, data):
        """
        Store the received data and write it back with a tilde appended.
        The tilde is appended so that the tests can verify that we processed
        the data.
        """
        self.data += data
        self.transport.write(data + b'~')

        Store the received data and write it back with a tilde appended.
        The tilde is appended so that the tests can verify that we processed
        the data.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_session.py