Guaranteed-order JSON dump in Python using collections.OrderedDict.

guaranteed_order_json.py

import json
from collections import OrderedDict


def serialize_with(collection_type):
    complex_object = collection_type()
    complex_object['z'] = collection_type()
    complex_object['z']['c'] = 30
    complex_object['z']['b'] = 20
    complex_object['z']['a'] = 10
    complex_object['y'] = '123'
    complex_object['x'] = []
    complex_object['x'].append(collection_type([
        ('c', 30),
        ('b', 20),
        ('a', 10),
    ]))
    complex_object['x'].append(collection_type([
        ('c', 300),
        ('b', 200),
        ('a', 100),
    ]))
    return complex_object


print json.dumps(serialize_with(dict), indent=4)
# Output:
# {
#     "y": "123",
#     "x": [
#         {
#             "a": 10,
#             "c": 30,
#             "b": 20
#         },
#         {
#             "a": 100,
#             "c": 300,
#             "b": 200
#         }
#     ],
#     "z": {
#         "a": 10,
#         "c": 30,
#         "b": 20
#     }
# }

print json.dumps(serialize_with(OrderedDict), indent=4)
# Output:
# {
#     "z": {
#         "c": 30,
#         "b": 20,
#         "a": 10
#     },
#     "y": "123",
#     "x": [
#         {
#             "c": 30,
#             "b": 20,
#             "a": 10
#         },
#         {
#             "c": 300,
#             "b": 200,
#             "a": 100
#         }
#     ]
# }