Python: parsing JSON-like Javascript data structures (w/ consecutive commas)

Question

I would like to parse JSON-like strings. Their lone difference with normal JSON is the presence of contiguous commas in arrays. When there are two such commas, it implicitly means that null should be inserted in-between. Example:

       JSON-like:  ["foo",,,"bar",[1,,3,4]]
      Javascript:  ["foo",null,null,"bar",[1,null,3,4]]
Decoded (Python):  ["foo", None, None, "bar", [1, None, 3, 4]]

The native json.JSONDecoder class doesn't allow me to change the behavior of the array parsing. I can only modify the parser for objects (dicts), ints, floats, strings (by giving kwargs functions to JSONDecoder(), please see the doc).

So, does it mean I have to write a JSON parser from scratch? The Python code of json is available but it's quite a mess. I would prefer to use its internals instead of duplicating its code!

Answer 1

Since what you're trying to parse isn't JSON per se, but rather a different language that's very much like JSON, you may need your own parser.

Fortunately, this isn't as hard as it sounds. You can use a Python parser generator like pyparsing. JSON can be fully specified with a fairly simple context-free grammar (I found one here), so you should be able to modify it to fit your needs.

Answer 2

Small & simple workaround to try out:

1. Convert JSON-like data to strings.
2. Replace ",," with ",null,".
3. Convert it to whatever is your representation.

4. Let JSONDecoder(), do the heavy lifting.

   1. & 3. can be omitted if you already deal with strings.

(And if converting to string is impractical, update your question with this info!)