[FIXED] How do I maintain the same structure when reading from, modifying and writing back to a JSON file?

Issue

I am currently reading in a JSON file, adding a key and writing it back out to the same file using this procedure

with open('data.json', 'r+') as f:
    data = json.load(f)
    temp_key={"test":"val"}
    data["test"]["new_key"] = temp_key
    f.seek(0)        # <--- should reset file position to the beginning.
    json.dump(data, f, indent=2)
    f.truncate()     # remove remaining part

(adopted from here)

but the issue is that it does not maintain order. for instance if I read in:

{
  "test": {
    "something": "something_else"
  },
  "abc": {
    "what": "huh"
  }
}

the output turns out as:

{
  "abc": {
    "what": "huh"
  },
  "test": {
    "something": "something_else",
    "new_key": {
      "test": "val"
    }
  }
}

When I would like it to be:

{
  "test": {
    "something": "something_else",
    "new_key": {
      "test": "val"
    }
  },
  "abc": {
    "what": "huh"
  }
}

I realise that JSON is a key/value based structure and the order does not matter, but is there a way of making the modification and maintaining the original structure?

Solution

As I said in a comment, you can use a collections.OrderedDict along with the optional object_pairs_hook keyword argument accepted by json.load() (in Python 2.7) to preserve the order of the original data when you rewrite the file.

This is what I meant:

#!/usr/bin/env python2
from collections import OrderedDict
import json


with open('ordered_data.json', 'r+') as f:
    data = json.load(f, object_pairs_hook=OrderedDict)
    temp_key = {"test": "val"}
    data["test"]["new_key"] = temp_key
    f.seek(0)  # Reset file position to the beginning.
    json.dump(data, f, indent=2)
    f.truncate()  # Remove remaining part.

Answered By - martineau