Equivalent of php isset in python

Question

Here is my python code:

if onerow[0]['result'] is None or not result['GetOdds'][0]['result']is None:

When result was empty, it returns this error:

if onerow[0]['result'] is None or not result['GetOdds'][0]['result']is None:
KeyError: 0

I want a something like php isset in python to check a dictionary item

Is there any equivalent function or class in python?

Solution

The method dict.get allows to safely get values from a dictionary.

d = {'foo': 1}
d.get('foo') # 1
d.get('bar') # None

You can also specify the default value you want dict.get to return if None happens to be a meaningful value.

sentinel = object()

d = {'foo': 1, 'baz': None}
d.get('bar', sentinel) # <object object at 0x...>

In your specific case, you have a KeyError when trying to access onerow[0]. You can use get to return None instead.

onerow.get(0) # None

Comments

[geoidesic]

what about tuples?

[geoidesic]

@Oliver Never mind I suppose it's a different question: how to test if a tuple exists. I did find the answer elsewhere.

[UselesssCat]

d.get('baz', 'default') will return None

[Olivier Melançon]

@UselesssCat that is why you create a sentinel object

[UselesssCat]

Maybe you are confusing 'baz' with 'bar'? As I understand the way to do is d.get('baz', 'default') or 'default'

[Olivier Melançon]

@UselesssCat No, I get that you mean 'baz'. Although, you want a way to differentiate between dict.get returning None because nothing was found and because the value is actually None. If that is not a concern, the first part of the answer works, if it is then you can create a sentinel object and compare to it. This way if None is returned you know the actual value was None while if the sentinel is returned, you know no value was found for that key.

[UselesssCat]

Thanks for explaining, I just understood what the sentinel object was for. Maybe if there was an if under line d.get('bar', sentinel) like if value is sentinel: print('value does'n exist'), it would have been clearer :P