def mark_notifications_as_read(self, last_read_at=datetime.datetime.utcnow()):
        """
        :calls: `PUT /notifications <https://developer.github.com/v3/activity/notifications>`_
        :param last_read_at: datetime
        """
        assert isinstance(last_read_at, datetime.datetime)
        put_parameters = {
            "last_read_at": last_read_at.strftime('%Y-%m-%dT%H:%M:%SZ')
        }

        headers, data = self._requester.requestJsonAndCheck(
            "PUT",
            "/notifications",
            input=put_parameters
        )