code: def add_to_group(self, group_id, nickname=None):
          
          if nickname is None:
              nickname = self.nickname
          memberships = Memberships(self.manager.session, group_id=group_id)
          return memberships.add(nickname, user_id=self.user_id)
docs: Add the member to another group.
  
          If a nickname is not provided the member's current nickname is used.
  
          :param str group_id: the group_id of a group
          :param str nickname: a new nickname
          :return: a membership request
          :rtype: :class:`MembershipRequest`