使用None作为键时json.dumps无法排序的类型

Question

When calling json.dumps on an object that contains a dictionary with a None and str type, how do I have it sort the results without throwing an exception? I'm trying it with sort_keys=True but that threw a TypeError . I don't care how None and bar are sorted relative to each other as long as it's consistent from run-to-run.

import json
foo = {None: 7, 'bar': 8}
json.dumps(foo)

which prints

'{"bar": 8, "null": 7}'

But then

json.dumps(foo, sort_keys=True)

prints

 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "C:\Program Files\Python35\lib\json\__init__.py", line 237, in dumps
     **kw).encode(obj)
   File "C:\Program Files\Python35\lib\json\encoder.py", line 198, in encode
     chunks = self.iterencode(o, _one_shot=True)
   File "C:\Program Files\Python35\lib\json\encoder.py", line 256, in iterencode
     return _iterencode(o, 0)
 TypeError: unorderable types: NoneType() < str()

Answer 1

Turns out a key of null is invalid JSON. Clearly, json.dumps(...) converts None keys to the string 'null' before returning, but presumably json.dumps(..., sort_keys=True) does the sorting before the conversion to a string.

One solution I found that allowed both sorting and displaying the structure in JSON is to convert it to JSON first, then sort the keys, like so:

import json

foo = {None: 7, 'bar': 8}
# {'bar': 8, None: 7}

foo_json = json.dumps(foo)
# '{"bar": 8, "null": 7}'

foo_prime = json.loads(foo_json)
# {'null': 7, 'bar': 8}

foo_sorted = json.dumps(foo_prime, sort_keys=True)
# '{"bar": 8, "null": 7}'

This does change the key (from None/null to 'null' ) but does so consistently.