Assign value to variable if no error

Question

I get from an API a Json object. The structure of the Json object might be different every time I run the script.

Let's say that "json_answer" is the json answer and I am looking for the value of the key 'data' that I want to store in "var", this key may not exist every time I run the script.

I would like to know if there is a shortcut for this code (one line):

try:
    var = json_answer['data']
except:
    var = None

EDIT :

Thank you for the answer, I already know about get. But I am looking very deep in the dictionary and I don't want to try all the "levels".

Let me clarify with this example :

dict = {'data':{'values':{'value':True}}}

print(dict['data']['values'].get('time', False)) # print false
print(dict['data']['values'].get('value', False)) # print True

I don't know in which level of the dict I might have a problem (the key exist or not). I just have this "PATH" ['data']['values']['value'] and if want to know if it exists or not. How can I do it with "get" ?

SOLUTION :

Based on @Ryan♦ solution and extended to JSON file that contains dict and list inside :

def _get(obj, keys, default=None):

    for key in keys:
        if isinstance(obj, dict):
            if key not in obj:
                return default
        elif isinstance(obj, list):
            if not len(obj) > key:
                return default
        else:
            return default
    obj = obj[key]
    return obj

Do you mean the 'data' key won’t exist every time? And is NULL supposed to be None? — Ry-
– Ry- ♦, Commented Jan 27, 2017 at 5:01

Ry- · Accepted Answer · 2017-01-27 08:20:29Z

2

There’s nothing built-in, but if you write a function for it, it’s rather nice:

def get_path(obj, keys, default=None):
    for key in keys:
        try:
            obj = obj[key]
        except (KeyError, IndexError):
            return default

    return obj

d = {'data': {'values': {'value': True}}}

print(get_path(d, ['data', 'values', 'time'], default=False))
print(get_path(d, ['data', 'values', 'value'], default=False))

edited Jan 27, 2017 at 8:20

answered Jan 27, 2017 at 5:54

Ry-♦

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2 Comments

Yassine Belmamoun Over a year ago

Hi Ryan, it works if the JSON file contains only dictionaries. Please check my update (section: Solution). Based on your function i added the "list" case.

Ry- Over a year ago

@YassineBelmamoun: I’m not sure which update you’re referring to, but see edit?

Mohammad Yusuf · Accepted Answer · 2017-01-27 08:18:04Z

2

Use .get(). It will return None when the key is not present

 var = json_answer.get('data')

If you want to specify a default value to the var variable when the key is not present you can specify it as a second argument to the .get() function.

 var = json_answer.get('data', 'default_value')

Demo:

import json

jsonobj = json.loads('{"a": "hello"}')
print jsonobj.get('a')
print jsonobj.get('b')
print jsonobj.get('b', "BYE")

Output:

hello
None
BYE

You can try something like this for your nested case.

c={}
d = {'data':{'values':{'value':True}}}
var1 = d.get('aa', c).get('bb', c).get('cc', c) or None
var2 = d.get('data', c).get('values', c).get('value', c)
print var1
print var2

Output:

None
True

edited Jan 27, 2017 at 8:18

answered Jan 27, 2017 at 5:02

Mohammad Yusuf

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4 Comments

Yassine Belmamoun Over a year ago

Thanks for the answer, i updated my question. Your solution works but not for my specific case.

Mohammad Yusuf Over a year ago

@YassineBelmamoun Check now. You will get None when the key is not found.

Yassine Belmamoun Over a year ago

It works, but it's not a pythonic solution. I think the best solution would be to use a function as described by Ryan. But thank you very much for your help.

Mohammad Yusuf Over a year ago

@YassineBelmamoun Agree that it's more Pythonic.

Andrew Magee · Accepted Answer · 2017-01-27 06:34:27Z

0

You could do this:

>>> d =  {'data': {'values': {'value': True}}}
>>> d.get('data', {}).get('values', {}).get('time', False)
False
>>> d.get('data', {}).get('values', {}).get('value', False)
True

answered Jan 27, 2017 at 6:34

Andrew Magee

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3 Comments

Yassine Belmamoun Over a year ago

It works, but it's not a pythonic solution. I think the best solution would be to use a function as described by Ryan since there is nothing built-in. But thank you very much for your help.

Andrew Magee Over a year ago

Why do you think it's not a Pythonic solution?

Yassine Belmamoun Over a year ago

I would like to avoid using three time the function "get" and repeat the definition of the default value. Thank you very much for your help.

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