python json keep object order on output

Question

class MessageCreator:

    def serialize(self,obj):
        return json.dumps(obj,sort_keys=False,indent=None, separators=(',', ':'))

    def createGroup(self,name,description,masterkey):
        return self.serialize({
                               'typ':str(types.CREATE_GROUP),
                               'group':[{
                                        'name':str(name),
                                        'descr':str(description),
                                        'mk':str(masterkey)
                                        }]
                            })

will return

{"group":[{"mk":"test","name":"test","descr":"test"}],"typ":"517"}

however i want the order to be kept intact like

{"typ":"517","group":[{"name":"test","descr":"test","mk":"test"}]}

How to achieve this?

Python dictionaries nor JSON objects have a defined order. They are always ordered arbitrarily. Why do you have to have a fixed order, what is your use case? — Martijn Pieters
– Martijn Pieters, Commented Feb 11, 2014 at 12:32
i specify a fixed order in a specification in order to compute signatures of payloads. — worenga
– worenga, Commented Feb 11, 2014 at 12:34
Then set sort_keys=True to ensure a stable key order. It doesn't matter to the consumer of this JSON what the order is, because they are allowed to use any order they like for the keys too. — Martijn Pieters
– Martijn Pieters, Commented Feb 11, 2014 at 12:36
or make your signature computer smarter about key ordering. Don't try to bend the JSON standard around this use-case. — Martijn Pieters
– Martijn Pieters, Commented Feb 11, 2014 at 12:37
@Tupteq: the JSON standard states that JSON objects use arbitrary order. The fact that the encoder just loops over dictionary items when encoding is merely a implementation detail. — Martijn Pieters
– Martijn Pieters, Commented Feb 11, 2014 at 12:41

Tupteq · Accepted Answer · 2014-02-11 12:51:36Z

2

You have to use OrderedDict, not a normal dict, because dict doesn't preserve order.

import json
from collections import OrderedDict

a = {'c':3, 'a':1, 'b':2}
print(json.dumps(a)) # Random order: a,c,b for example
a = OrderedDict([('c', 3), ('a', 1), ('b', 2)])
print(json.dumps(a))  # Desired order: c,a,b

edited Feb 11, 2014 at 12:51

answered Feb 11, 2014 at 12:35

Tupteq

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Comments

Noufal Ibrahim · Accepted Answer · 2014-02-11 12:33:38Z

1

If you want order, use a list([]). If you want random access, use a table({}). You can keep a list of keys in order as a separate attribute and then resort by that after you read out the data.

answered Feb 11, 2014 at 12:33

Noufal Ibrahim

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Comments

iurisilvio · Accepted Answer · 2014-02-11 12:38:14Z

1

Use an OrderedDict instead of a normal dict.

import json
from collections import OrderedDict

print json.dumps(OrderedDict([('a', 1), ('b', 2)]))

answered Feb 11, 2014 at 12:38

iurisilvio

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Comments

venpa · Accepted Answer · 2014-02-11 12:41:03Z

1

you can do this:

import collections
data = (("typ","517"),
    ("group",[{"mk":"test","name":"test","descr":"test"}]))
od = collections.OrderedDict(data)

answered Feb 11, 2014 at 12:41

venpa

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Comments

Sar009 · Accepted Answer · 2014-02-11 12:53:18Z

0

change serialize() as follow

from collections import OrderedDict
order=["typ", "group"]
def serialize(obj):
    temp_list=OrderedDict()
    for each_order in order:
        temp_list[each_order]=obj[each_order]
    return json.dumps(temp_list)

edited Feb 11, 2014 at 12:53

answered Feb 11, 2014 at 12:48

Sar009

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1 Comment

worenga Over a year ago

the order is also required for subdicts

manjy · Accepted Answer · 2023-06-27 10:50:13Z

0

As of Python 3.7, dictionaries will retain its order. From Python 3.7 Changelog

the insertion-order preservation nature of dict objects has been declared to be an official part of the Python language spec.

answered Jun 27, 2023 at 10:50

manjy

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