Clean/update the cache of all the tasks for a given course (id)
        :param courseid:

def update_cache_for_course(self, courseid):
        """
        Clean/update the cache of all the tasks for a given course (id)
        :param courseid:
        """
        to_drop = []
        for (cid, tid) in self._cache:
            if cid == courseid:
                to_drop.append(tid)
        for tid in to_drop:
            del self._cache[(courseid, tid)]