code: def invalidate_permissions_cache(self):
          
          if self.user:
              self.user._authority_perm_cache_filled = False
          if self.group:
              self.group._authority_perm_cache_filled = False
docs: In the event that the Permission table is changed during the use of a
          permission the Permission cache will need to be invalidated and
          regenerated. By calling this method the invalidation will occur, and
          the next time the cached_permissions is used the cache will be
          re-primed.