code: def can_unsubscribe_from_topic(self, topic, user):
          
          # A user can unsubscribe from topics if they are authenticated and if they have the
          # permission to read the related forum. Of course a user can unsubscribe only if they are
          #  already a subscriber of the considered topic.
          return (
              user.is_authenticated and
              topic.has_subscriber(user) and
              self._perform_basic_permission_check(topic.forum, user, 'can_read_forum')
          )
docs: Given a topic, checks whether the user can remove it from their subscription list.