How to custom-sort a list of dict to use in json.dumps

Question

I have a list similar to

allsites = [     {         'A5': 'G',          'A10': 'G',          'site': 'example1.com',          'A1': 'G'     },      {         'A5': 'R',          'A10': 'Y',         'site': 'example2.com',          'A1': 'G'     } ] 

Which I use in a json.dumps:

data = { 'Author':"joe", 'data':allsites } print json.dumps(data,sort_keys=True,indent=4, separators=(',', ': ')) 

This outputs the following JSON:

{     "Author": "joe",     "data": [         {             "A1": "G",             "A10": "G",             "A5": "G",             "site": "example1.com"         },         {             "A1": "G",     (...) 

I would like the "data" section of this JSON string to be sorted via a custom key ("alphabet"), in the case above this would be site, A1, A5, A10 and actually look like:

{     "Author": "joe",     "data": [         {             "site": "example1.com",             "A1": "G",             "A5": "G",             "A10": "G"         },         {             "site": "example2.com",             "A1": "G",     (...) 

I read about custom sorting in the Sorting FAQ but it just gives a way to override the comparison function, not to mention that I do not know how to insert this into my code.

How to do that?

Answer 1

Since python dicts are unordered collections, use collections.OrderedDict with a custom sort:

from collections import OrderedDict import json  allsites = [     {         'A5': 'G',         'A10': 'G',         'site': 'example1.com',         'A1': 'G'     },     {         'A5': 'R',         'A10': 'Y',         'site': 'example2.com',         'A1': 'G'     } ]  sort_order = ['site', 'A1', 'A5', 'A10'] allsites_ordered = [OrderedDict(sorted(item.iteritems(), key=lambda (k, v): sort_order.index(k)))                     for item in allsites]  data = {'Author': "joe", 'data': allsites_ordered} print json.dumps(data, indent=4, separators=(',', ': ')) 

prints:

{     "data": [         {             "site": "example1.com",             "A1": "G",             "A5": "G",             "A10": "G"         },         {             "site": "example2.com",             "A1": "G",             "A5": "R",             "A10": "Y"         }     ],     "Author": "joe" }