How to make a python dictionary key error return false

Question

I am dealing with JSON data sets with dynamic response structures (keys) and need to execute code if certain keys exist. Right now if the key doesn't exist it throws a key error which I have attempted to pass through a bool operand but it appears the key error trumps bool operands in Python.

bool(dictionary['key'])

KeyError: 'key'

I feel like there is some way to do this that's easier than I'm attempting but just haven't been able to find anything through researching. Any help would be greatly appreciated.

Rushy Panchal · Accepted Answer · 2016-04-30 22:14:40Z

9

You want dictionary.get('key'). By default, this returns None, which will evaluate as False.

answered Apr 30, 2016 at 22:14

Rushy Panchal

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5 Comments

Jack Burton Over a year ago

That is a great method for when a dictionary is shallow however JSON data sets can be heavily layered and I need something that iterates through the entire data structure to check for keys 2 or 3 levels deep at times. Is there a simple way to do that?

user2285236 Over a year ago

@JackBurton try / except KeyError: might be useful for that.

Rushy Panchal Over a year ago

@JackBurton Do you mean that you want a function to recursively check for a key? That's significantly more complex, and you probably don't want that sort of search everytime you want the key value.

Jack Burton Over a year ago

@RushyPanchal Correct. The JSON structure is like this: {dictionary1 {dictionary2 [list {dictionary3}] } } I am after the keys in dictionary3 which may or may not exist for each item in the list. There could be several iterations of dictionary3 within the list object.

martineau Over a year ago

Jack: You need to show the structure of the dictionary being searched and revise your question (and its title) to reflect your real question.

danidee · Accepted Answer · 2016-04-30 22:12:42Z

1

use dict.get and set a default value if the key was not found

dictionary.get('key', 'NotFound')

answered Apr 30, 2016 at 22:12

danidee

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Comments

Perry · Accepted Answer · 2016-04-30 22:17:21Z

0

Have you tried using dictionary.has_key(key_name) this method will return true if the key exists and false if it doesn't.

edited Apr 30, 2016 at 22:17

Perry

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answered Apr 30, 2016 at 22:17

Rajat Kusumwal

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1 Comment

Jan Vlcinsky Over a year ago

Better use key_name in dictionary test.

aghast · Accepted Answer · 2016-04-30 22:53:02Z

Did you want something like this?

#!python3
json_data = [
        { 'key1':
            { 'key2':
                [
                    {'key3': 1 }
                    ]
                }
            }
        ]

def get_deep(*keys):
    try:
        doa = json_data
        for key in keys:
            doa = doa[key]
        return doa
    except KeyError:
        return None
    except IndexError:
        return None

tests = (
    # Want, Keys...
    (1, 0, 'key1', 'key2', 0, 'key3'),
    (None, 1, 'key1', 'key2', 0, 'key3'),
    (None, 0, 'key11', 'key2', 0, 'key3'),
    (None, 0, 'key1', 'key22', 0, 'key3'),
    (None, 0, 'key1', 'key2', 1, 'key3'),
    (None, 0, 'key1', 'key2', 0, 'key33'),
)


for i,test in enumerate(tests):
    expected,*keys = test
    got = get_deep(*keys)
    if got is expected:
        print(i, "OK")
    else:
        print(i, "FAIL", got, "is not", expected)

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