使用gremlin_python的client实例时报'NoneType无processor属性'错误如何解决？

我使用Jupyter Notebook对Neptune Database执行gremlin查询，先从MySQL数据库获取信息生成gremlin查询字符串，再通过gremlin_python库的Client模块执行，相关代码如下：

def getConnectionWithNeptuneGraphDB():
    global clientt
    if clientt is not None:
        print('clientt instance is available')
    else:
        print('clientt is not available')
        clientt = client.Client('neptune_db_endpoint', 'g')
    return clientt

# 创建Person节点的函数
def createPersonNode():
    personsInfo = getPersonInformation(companyIdTouple)
    print(personsInfo)
    personGremQry = queryToCreatePersonNode(personsInfo)
    clientt = getConnectionWithNeptuneGraphDB()
    clientt.submit(personGremQry)
    #print(personsInfo)
    print('Person Node created successfully')

def main():
    # 创建Company节点流程
    createCompanyNode()
    # 创建Person节点流程
    createPersonNode()      
    connection.close()
    clientt.close()

main()函数为入口点，执行时createCompanyNode()运行正常，可成功将公司数据写入数据库，但执行createPersonNode()时会抛出如下错误，即便单独执行createPersonNode()也会出现相同报错：

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-558-263240bbee7e> in <module>
----> 1 main()

<ipython-input-557-e622c1b6eefc> in main()
      1 def main():
      2     #createCompanyNode()
----> 3     createPersonNode()
      4     connection.close()
      5     clientt.close()

<ipython-input-550-60763852d6da> in createPersonNode()
     16     personGremQry = queryToCreatePersonNode(personsInfo)
     17     clientt = getConnectionWithNeptuneGraphDB()
---> 18     clientt.submit(personGremQry)
     19     #print(personsInfo)
     20     print('Person Node created successfully')

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/client.py in submit(self, message, bindings, request_options)
    128 
    129     def submit(self, message, bindings=None, request_options=None):
--> 130         return self.submitAsync(message, bindings=bindings, request_options=request_options).result()
    131 
    132     def submitAsync(self, message, bindings=None, request_options=None):

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
    423                 raise CancelledError()
    424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
    426 
    427             self._condition.wait(timeout)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in __get_result()
    382     def __get_result(self):
    383         if self._exception:
--> 384             raise self._exception
    385         else:
    386             return self._result

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/connection.py in cb(f)
     64         def cb(f):
     65             try:
--- > 66                 f.result()
     67             except Exception as e:
     68                 future.set_exception(e)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
    423                 raise CancelledError()
    424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
    426 
    427             self._condition.wait(timeout)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/_base.py in __get_result()
    382     def __get_result(self):
    383         if self._exception:
--> 384             raise self._exception
    385         else:
    386             return self._result

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/concurrent/futures/thread.py in run(self)
     54 
     55         try:
--- > 56             result = self.fn(*self.args, **self.kwargs)
     57         except BaseException as exc:
     58             self.future.set_exception(exc)

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/protocol.py in write(self, request_id, request_message)
     72     def write(self, request_id, request_message):
     73         message = self._message_serializer.serialize_message(
--- > 74             request_id, request_message)
     75         self._transport.write(message)
     76 

~/anaconda3/envs/JupyterSystemEnv/lib/python3.6/site-packages/gremlin_python/driver/serializer.py in serialize_message(self, request_id, request_message)
    134 
    135     def serialize_message(self, request_id, request_message):
--> 136         processor = request_message.processor
    137         op = request_message.op
    138         args = request_message.args

AttributeError: 'NoneType' object has no attribute 'processor'

这个错误是client.submit()方法接收到的输入无法被解析为合法的gremlin请求，导致内部生成了空的请求消息对象，访问processor属性时触发报错，可按以下步骤排查解决：

• 首先检查queryToCreatePersonNode(personsInfo)的返回值：在生成personGremQry后添加打印语句print(type(personGremQry), personGremQry)，如果返回值为None，说明查询生成函数逻辑存在问题，没有正确返回构造完成的gremlin语句，修复生成逻辑返回合法字符串即可。
• 如果返回值为字符串，检查字符串语法是否正确：从MySQL取出的人员信息如果包含未转义的单引号、双引号、换行符等特殊字符，会导致构造的gremlin语句语法损坏。可以把打印出来的查询字符串直接放到Neptune控制台执行，验证是否能正常运行，若控制台执行也报错，就先修复查询语法，对特殊字符做转义处理。
• 检查gremlin_python版本兼容性：部分旧版本gremlin_python和新版Neptune服务端存在兼容问题，若以上两点都排查无问题，可以升级gremlin_python到和Neptune服务端匹配的稳定版本，比如3.4.x或3.5.x系列。
• 额外优化建议：当前全局复用client的写法存在连接失效的隐患，推荐每次使用后关闭连接，或者用连接池方式管理连接，避免偶发的连接异常问题。

内容的提问来源于stack exchange，提问作者Ranjit Soni