motor_beginning.py

class MessagesHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        db = self.settings['db']
        self._response_buffer = []
        db.messages.find().sort([('_id', -1)]).each(self._found_callback)

    def _found_callback(self, message, error):
        if error:
            raise tornado.web.HTTPError(500, error)
        elif message:
            self._response_buffer.append({
                'id': message['_id'], 
                'msg': message['msg']
            })
        else:
            # Iteration complete
            self.finish({"data": self._response_buffer})