使用isinstance捕获NoneType错误

Question

我有下面的代码，但是not isinstance()并没有像预期的那样工作。

<ipython-input-94-009e9fb4f54a> in extract(self, row)
     34             event_payload_json = json.loads(row.event_payload)
     35             #print(event_payload_json['payload']['info']['work'])
---> 36             if not isinstance(event_payload_json['payload']['info']['work'], type(None)):
     37                 if "test_statement" not in event_payload_json['payload']['info']['work']:
     38                     decoded_str = base64.b64decode(<>)

TypeError: 'NoneType' object is not subscriptable

如果event_payload_json['payload']['info']['work']不是NoneType，那么我的意图就是不解码，但是它并没有像预期的那样工作。任何帮助都将不胜感激！

Answer 1

在Python中，没有一个是单例，所以可以这样做：

if event_payload_json['payload']['info']['work'] is not None:

另外，如果event_payload_json['payload']['info']['work']只接受真实值，那么就足够像这样检查它了。

if event_payload_json['payload']['info']['work']:

Answer 2

错误告诉您您尝试订阅None，所以event_payload_json['payload']或event_payload_json['payload']['info']都是None。处理该错误的最简单方法是将语句放在try/ put块中并捕获TypeError。结果表明，试图查看字符串是否在None中也是一个TypeError，因此您可以同时处理所有的情况。

event_payload_json = json.loads(row.event_payload)
#print(event_payload_json['payload']['info']['work'])
try:
    work = event_payload_json['payload']['info']['work']
    if "test_statement" not in work:
        decoded_str = base64.b64decode(work)
except TypeError:
    pass