Testing for None throws an error the attribute doesn't exist

Question

----> 1 if person.network is None:
      2     print('person.network does not exist')
      3 

AttributeError: 'Person' object has no attribute 'network'

As you can see on line 1, I'm checking if 'network' doesn't exist. However, when it doesn't exist it fails and throws a python error. I'm a bit lost as to how this is happening. Shouldn't line 1 catch this exact problem?

The actual code properly goes through about 10 records before failing when one of them doesn't have 'network' defined.

An attribute that doesn't exist is different from an attribute set to None. — user2357112, Nov 06 '17 at 21:32
you are probably looking to do something like [this](https://stackoverflow.com/questions/610883/how-to-know-if-an-object-has-an-attribute-in-python). — R Nar, Nov 06 '17 at 21:32
Sounds like a data dependent issue tied to your specific code. You'll need to provide more context to debug why the buggy instance is raising the exception. — jxramos, Nov 06 '17 at 21:34

Dflip240 · Answer 1 · 2017-11-06T21:51:58.363

3

You can use the built in python function hasattr :

    if hasattr(person, "network") :

edited Nov 06 '17 at 21:51

answered Nov 06 '17 at 21:33

Dflip240

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1
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score 3 · Accepted Answer · answered Nov 06 '17 at 21:34

There is a difference between an instance attribute having the value of None and it not existing at all (your case). To properly check whether an instance attribute exist, you can use the hasattr() method:

if hasattr(person, "network"):
    # do stuff

If you need to retrieve the value, you can do so safely using getattr():

network = getattr(person, "network", None)

The last parameter is the default value to be returned in case person does not have the network attribute.

Greatly appreciate the clarification! – mauvehed Nov 06 '17 at 21:45 — mauvehed, Nov 06 '17 at 21:45

Testing for None throws an error the attribute doesn't exist

2 Answers2