def METHOD_NAME(self, fd):
    """Register/unregister an fd with the poller."""
    try:
        self._poller.unregister(fd)
    except KeyError:
        pass
    mask = 0
    if fd in self._reads:
        mask = mask | POLLIN
    if fd in self._writes:
        mask = mask | POLLOUT
    if mask != 0:
        self._poller.register(fd, mask)
    else:
        if fd in self._selectables:
            del self._selectables[fd]