Ordering a nested dictionary in python with json format

[UmarAsghar]

BPO	38414
Nosy	@serhiy-storchaka
Files	test.py bug.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-10-09.06:18:06.400>
created_at = <Date 2019-10-08.19:57:40.123>
labels = ['type-feature']
title = 'Ordering a nested dictionary in python with json format'
updated_at = <Date 2019-10-09.06:18:06.395>
user = 'https://bugs.python.org/UmarAsghar'

bugs.python.org fields:

activity = <Date 2019-10-09.06:18:06.395>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2019-10-09.06:18:06.400>
closer = 'serhiy.storchaka'
components = []
creation = <Date 2019-10-08.19:57:40.123>
creator = 'Umar Asghar'
dependencies = []
files = ['48649', '48650']
hgrepos = []
issue_num = 38414
keywords = []
message_count = 5.0
messages = ['354228', '354229', '354230', '354237', '354251']
nosy_count = 2.0
nosy_names = ['serhiy.storchaka', 'Umar Asghar']
pr_nums = []
priority = 'normal'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue38414'
versions = ['Python 2.7']

[UmarAsghar]

Python does not preserve ordering in JSON format. I have tested it out but it's not working. Here is my code.

# Python3 code to demonstrate 
# Sort nested dictionary by key 
# using OrderedDict() + sorted() 
from collections import OrderedDict 
from operator import getitem 
import json

# initializing dictionary 
test_dict = {'Nikhil' : { 'roll' : 24, 'marks' : 17}, 
            'Akshat' : {'roll' : 54, 'marks' : 12}, 
            'Akash' : { 'roll' : 12, 'marks' : 15}} 

# printing original dict 
print("The original dictionary : " + str(test_dict)) 

# using OrderedDict() + sorted() 
# Sort nested dictionary by key 
res = OrderedDict(sorted(test_dict.items(), 
    key = lambda x: getitem(x[1], 'marks'))) 

print("The sorted dictionary by marks is : " + str(res))
# Output
# The sorted dictionary by marks is : OrderedDict([('Akshat', {'marks': 12, 'roll': 54}), ('Akash', {'marks': 15, 'roll': 12}), ('Nikhil', {'marks': 17, 'roll': 24})])

res = json.dumps(res)

# print result
print("The sorted dictionary by marks is : (json)")
print(json.loads(res))
# Output
# The sorted dictionary by marks is :
# {'Akash': {'marks': 15, 'roll': 12}, 'Akshat': {'marks': 12, 'roll': 54}, 'Nikhil': {'marks': 17, 'roll': 24}}
Does anyone suggest any solution for it?

It's different than a simple dictionary. It only targets the nested dictionary ordering. Please don't mark it a duplication of simple dictionary ordering with JSON. thanks

[UmarAsghar]

I guess it exists in all Python versions. I have tested in both Python 2 and Python 3.

Python 2.7.15+ (default, Jul 9 2019, 16:51:35)
[GCC 7.4.0] on linux2

Python 3.6.8 (default, Aug 20 2019, 17:12:48)
[GCC 8.3.0] on linux

[UmarAsghar]

I have recently attached the file, please review it as a code reference.

[UmarAsghar]

Please ignore the above shared sample data in the above code and consider this one.

this is the exact code that is misbehaving in python 2.7

# Sort nested dictionary by key
# using OrderedDict() + sorted()
from collections import OrderedDict
from operator import getitem
import json

# initializing dictionary
test_dict = {'3' : { 'roll' : 24, 'marks' : 17},
            '2' : {'roll' : 54, 'marks' : 12},
            '1' : { 'roll' : 12, 'marks' : 15}}

# printing original dict
print("The original dictionary : " + str(test_dict))

# using OrderedDict() + sorted()
# Sort nested dictionary by key
res = OrderedDict(sorted(test_dict.items(),
    key = lambda x: getitem(x[1], 'marks')))

print("The sorted dictionary by marks is : " + str(res))
# Output
# The sorted dictionary by marks is : OrderedDict([('2', {'roll': 54, 'marks': 12}), ('1', {'roll': 12, 'marks': 15}), ('3', {'roll': 24, 'marks': 17})])

res1 = json.dumps(res)

# print result
print("The sorted dictionary by marks is : (json)")
print(json.loads(res1))
# Output
# The sorted dictionary by marks is : (json)
# {u'1': {u'roll': 12, u'marks': 15}, u'3': {u'roll': 24, u'marks': 17}, u'2': {u'roll': 54, u'marks': 12}}

[serhiy-storchaka]

Dictionary preserve the insertion order starting from Python 3.7 (actually from 3.6, but it was not guarantied). I am surprised that you got different result in 3.6. I cannot reproduce it.

In older Python versions you can pass object_pairs_hook=OrderedDict to json.loads() to preserve the insertion order. The regular dictionary cannot preserve it, by its structure.