def iterate(self):
        """
        Call C{doRead} and C{doWrite} on all readers and writers respectively.
        """
        for reader in list(self._readers):
            self._doReadOrWrite(reader, reader, self._POLL_IN)
        for writer in list(self._writers):
            self._doReadOrWrite(writer, writer, self._POLL_OUT)

        Call C{doRead} and C{doWrite} on all readers and writers respectively.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/posixbase.py