code: def update_cache_for_course(self, 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)]
docs: Clean/update the cache of all the tasks for a given course (id)
          :param courseid: