How to convert Python dict to JSON when some keys are not strings?

Question

The JSON equivalent of a Python dict is a JSON object. However its keys must be strings, that's a well-known limitation.

I need to support also boolean and numeric keys. I could make a simple Python value <--> JSON string one-to-one translation:

False <--> "bool:False"
42 <--> "int:42"
"Foo" <--> "str:Foo"

But I'd like to ask if there is some existing recommendation or some kind of standard for this. Simply anything that it is worth to be compatible with.

i think you can just omit bool:, int:, str: to make it simpler. — Shiping, Jan 25 '17 at 20:16
I suppose that you could do `bool(False)`, `int(42)` and use `eval`. — Jean-François Fabre, Jan 25 '17 at 20:16
For JSON, not that I know of. You could instead use msgpack or some other format that works the way you want. — Blender, Jan 25 '17 at 20:16
Here's some discussion that you may find valuable http://stackoverflow.com/q/1450957/1916449 — arekolek, Jan 25 '17 at 20:46
Or maybe `{'{}:{}'.format(type(k).__name__, str(k)): v for k, v in d.items()}` — Patrick Haugh, Jan 25 '17 at 20:52

score 1 · Accepted Answer · answered Jan 25 '17 at 20:34

1

JSON isn't able to do that and I don't know of any widely-used extensions of JSON that allow you to do this. You'd have to write the serializer and deserializer yourself, which probably wouldn't be that difficult if you subclass json.JSONEncoder and json.JSONDecoder.

If you're able to switch protocols, there are JSON-ish protocols that support non-string keys. MessagePack is one:

>>> import msgpack
>>> msgpack.loads(msgpack.dumps({'1': 12, False: 3, 2: 8}))
{False: 3, 2: 8, '1': 12}

answered Jan 25 '17 at 20:34

Blender

289,723
53
439
496

Thank you for your suggestion.This time I need to make a change as small as possible to an existing system, so I must stay with JSON. +1 because I learned someting new. – VPfB Jan 25 '17 at 21:14
"_I don't know of any widely-used extensions of JSON that allow you to do this_" is accepted as a direct answer to my question. – VPfB Jan 26 '17 at 11:16

score 0 · Answer 2 · answered Jan 25 '17 at 20:31

0

This would achieve what you want:

>>> import json
>>> data = {False: 'this data', 42: 'answer', 'foo': 'bar'}
>>> json.dumps({"%s:%s" % (type(k).__name__, k): v for k, v in data.items()})
'{"int:42": "answer", "str:foo": "bar", "bool:False": "this data"}'

You'd then have to de-serialize this, and it would only work for basic types.

answered Jan 25 '17 at 20:31

Rafael Barros

2,738
1
21
28

Yes, something like this will do. However there are many possible variations. I just wanted to know, if some format is already in use or otherwise preferred. It looks like the answer is negative, but that's a valid answer. – VPfB Jan 25 '17 at 21:24

score 0 · Answer 3 · answered Jan 25 '17 at 20:38

0

Since you cannot issue standard JSON, why don't you just use str to serialize and ast.literal_eval (standard package) to deserialize?

>>> d = {'a': 33, 23:(4,5), False: 10, 4: "foo"}
>>> a = str(d)   # convert the python structure to a string
>>> d2 = ast.literal_eval(a)
>>> print(d2)  # evaluate the a literal to a python structure
{False: 10, 4: 'foo', 'a': 33, 23: (4, 5)}
>>> d2 == d   # are those the same before & after evaluation ?
True

answered Jan 25 '17 at 20:38

Jean-François Fabre

137,073
23
153
219

Thank you for your suggestion.This time I need to make a change as small as possible to an existing system, so I must stay with JSON. – VPfB Jan 25 '17 at 21:15

How to convert Python dict to JSON when some keys are not strings?

3 Answers3