def addWriter(self, writer):
        """
        Add a FileDescriptor for notification of data available to write.
        """
        try:
            self._add(writer, self._writes, self._reads, self._selectables,
                      EPOLLOUT, EPOLLIN)
        except IOError as e:
            if e.errno == errno.EPERM:
                # epoll(7) doesn't support certain file descriptors,
                # e.g. filesystem files, so for those we just poll
                # continuously:
                self._continuousPolling.addWriter(writer)
            else:
                raise

        Add a FileDescriptor for notification of data available to write.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/epollreactor.py