Python's json module, converts int dictionary keys to strings

user_176166 0
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I have found that when the following is run, python's json module (included since 2.6) converts int dictionary keys to strings.

>>> import json
>>> releases = {1: "foo-v0.1"}
>>> json.dumps(releases)
'{"1": "foo-v0.1"}'

Is there any easy way to preserve the key as an int, without needing to parse the string on dump and load. I believe it would be possible using the hooks provided by the json module, but again this still requires parsing. Is there possibly an argument I have overlooked? cheers, chaz

Sub-question: Thanks for the answers. Seeing as json works as I feared, is there an easy way to convey key type by maybe parsing the output of dumps? Also I should note the code doing the dumping and the code downloading the json object from a server and loading it, are both written by me.

python json
9 Answers

Here is my solution! I used object_hook, it is useful when you have nested json

>>> import json
>>> json_data = '{"1": "one", "2": {"-3": "minus three", "4": "four"}}'
>>> py_dict = json.loads(json_data, object_hook=lambda d: {int(k) if k.lstrip('-').isdigit() else k: v for k, v in d.items()})

>>> py_dict
{1: 'one', 2: {-3: 'minus three', 4: 'four'}}

There is filter only for parsing json key to int. You can use int(v) if v.lstrip('-').isdigit() else v filter for json value too.

user_83236500

Convert the dictionary to be string by using str(dict) and then convert it back to dict by doing this:

import ast
ast.literal_eval(string)
user_70691080

I made a very simple extension of Murmel's answer which I think will work on a pretty arbitrary dictionary (including nested) assuming it can be dumped by JSON in the first place. Any keys which can be interpreted as integers will be cast to int. No doubt this is not very efficient, but it works for my purposes of storing to and loading from json strings.

def convert_keys_to_int(d: dict):
    new_dict = {}
    for k, v in d.items():
        try:
            new_key = int(k)
        except ValueError:
            new_key = k
        if type(v) == dict:
            v = _convert_keys_to_int(v)
        new_dict[new_key] = v
    return new_dict

Assuming that all keys in the original dict are integers if they can be cast to int, then this will return the original dictionary after storing as a json. e.g.

>>>d = {1: 3, 2: 'a', 3: {1: 'a', 2: 10}, 4: {'a': 2, 'b': 10}}
>>>convert_keys_to_int(json.loads(json.dumps(d)))  == d
True
user_126209050
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