Why do int keys of a python dict turn into strings when using json.dumps?

Question

According to this conversion table, Python ints get written as JSON numbers when serialized using the JSON module--as I would expect and desire.

I have a dictionary with an integer key and integer value:

>>> d = {1:2} >>> type(d.items()[0][0]) <type 'int'> >>> type(d.items()[0][1]) <type 'int'> 

When I use the json module to serialize this to a JSON string, the value is written as a number, but the key is written as a string:

>>> json.dumps(d) '{"1": 2}' 

This isn't the behavior I want, and it seems particularly broken since it breaks json.dumps/json.loads round-tripping:

>>> d == json.loads(json.dumps(d)) False 

Why does this happen, and is there a way I can force the key to be written as a number?

Answer 1

The simple reason is that JSON does not allow integer keys.

object     {}     { members }  members     pair     pair , members pair     string : value  # Keys *must* be strings. 

As to how to get around this limitation - you will first need to ensure that the receiving implementation can handle the technically-invalid JSON. Then you can either replace all of the quote marks or use a custom serializer.