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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def modify(self, fd, eventmask):
 """ Change the bit-mask of events associated with a previously-registered descriptor. :param fd: The descriptor to modify. :param eventmask: New bit-mask of events that will be monitored. :raises ValueError: If :meth:`closed()` is True :raises OSError: If the underlying ``epoll_ctl(2)`` fails. The error message matches those found in the manual page. """

        if self._epfd < 0:
            _err_closed()
        ev = epoll_event()
        ev.events = eventmask
        ev.data.fd = fd
        epoll_ctl(self._epfd, EPOLL_CTL_MOD, fd, byref(ev))