def userJoined(group, user):
        """
        Callback notifying this user that the given user has joined
        the given group.

        @type group: L{IGroup}
        @type user: L{IUser}

        @rtype: L{twisted.internet.defer.Deferred}
        """

        Callback notifying this user that the given user has joined
        the given group.

        @type group: L{IGroup}
        @type user: L{IUser}

        @rtype: L{twisted.internet.defer.Deferred}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/words/iwords.py