@tornado.gen.coroutine
    def prepare(self):
        yield self.find_current_session()
        if self.tw_load_portlink:
            portid = self.get_cookie('tworld_portlink', None)
            if portid:
                # Load up the portlink data, if possible. (If it's not 
                # possible, don't worry too much.)
                try:
                    portid = ObjectId(portid)
                    self.twportlink = yield self.external_portal_description(portid)
                except Exception as ex:
                    self.application.twlog.info('Unable to load portlink info for template: %s', ex)
Called before every get/post invocation for this handler. We use
dataset/ETHPy150Open erkyrath/tworld/lib/tweblib/handlers.py/MyHandlerMixin.prepare