Order is not preserved when OrderedDict is returned from view.

[mamalos]

With Cornice versions 3.6 and 3.7-dev, when returning an OrderedDict, the order of the parameters is not preserved in the returned request.

Ie. if we have the following code:

from cornice import Service
from collections import OrderedDict

test_ordered_service = Service(name='testorderedservice',
                    path='/testorderedservice',)

test_unordered_service = Service(name='testunorderedservice',
                    path='/testunorderedservice',)


@test_ordered_service.get()
def return_ordered_stuff(request):
    ret = OrderedDict([
        ('datefrom', '2019-07-17'),
        ('dateto', '2019-07-23'),
        ('origin', 'test'),
        ('overall_usage', []),
        ('pop_usage', {}),
        ('hit_usage', 5),
        ('bandwidth_usage', 3160)])
    return ret


@test_unordered_service.get()
def return_unordered_stuff(request):
    ret = {'datefrom': '2019-07-17',
           'dateto': '2019-07-23',
           'origin': 'test',
           'overall_usage': [],
           'pop_usage': {},
           'hit_usage': 5,
           'bandwidth_usage': 3160}
    return ret

Then we're getting the following results:

$ curl -X GET http://localhost:6543/testorderedservice | python -m json.tool 

{
    "bandwidth_usage": 3160,
    "datefrom": "2019-07-17",
    "dateto": "2019-07-23",
    "hit_usage": 5,
    "origin": "test",
    "overall_usage": [],
    "pop_usage": {}
}

$ curl -X GET http://localhost:6543/testunorderedservice | python -m json.tool

{
    "bandwidth_usage": 3160,
    "datefrom": "2019-07-17",
    "dateto": "2019-07-23",
    "hit_usage": 5,
    "origin": "test",
    "overall_usage": [],
    "pop_usage": {}
}

I realised this problem when I was running cornice with marshmallow validators, where my output was not in the expected order and I was suspecting it was a marshmallow problem, which eventually was not the case.