在appengine数据存储区我得到异常错误，但事务工作。怎么回事？

Question

class registerPage(webapp2.RequestHandler):
    def post(self):
        deviceID = cgi.escape(self.request.get('deviceID'))
        PNID = cgi.escape(self.request.get('PNID'))
        try:
            user = RegisteredUser.get_or_insert(deviceID)
            user.push_notification_ID = PNID
            try:
                user.put()
                self.response.headers['Content-Type'] = "text/plain"
                self.response.set_status(201)
                logging.info("DeviceID = %s",newUser.key().name())
            except Timeout:
                logging.error("Timeout:%s unable to put user",deviceID)
            except TransactionFailedError:
                logging.error("TransactionFailedError:%s unable to put user",deviceID)
            except InternalError:
                logging.error("InternalError:%s unable to put user",deviceID)
        except:
            logging.error("%s unable to save Push Notification",deviceID)
            self.response.headers['Content-Type'] = "text/plain"
            self.response.set_status(204)

我不太明白为什么我在最外层的范围内获得异常，即调用get_or_insert时。交易成功了。我很确定它有效但我可以检索实体并看到新的实体已被添加。有人会知道发生了什么吗？