def addReader(self, reader):
        """Add a FileDescriptor for notification of data available to read.
        """
        fd = reader.fileno()
        if fd not in self._reads:
            self._selectables[fd] = reader
            self._reads[fd] =  1
            self._updateRegistration(fd)
Add a FileDescriptor for notification of data available to read.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/pollreactor.py