Background: I want to store a dict object in json format that has say, 2 entries:

(1) Some object that describes the data in (2). This is small data mostly definitions, parameters that control, etc. and things (maybe called metadata) that one would like to read before using the actual data in (2). In short, I want good human readability of this portion of the file.

(2) The data itself is a large chunk- should more like machine readable (no need for human to gaze over it on opening the file).

Problem: How to specify some custom indent, say 4 to the (1) and None to the (2). If I use something like json.dump(data, trig_file, indent=4) where data = {'meta_data': small_description, 'actual_data': big_chunk}, meaning the large data will have a lot of whitespace making the file large.

CodePudding user response：

Assuming you can append json to a file:

1. Write {"meta_data":\n to the file.
2. Append the json for small_description formatted appropriately to the file.
3. Append ,\n"actual_data":\n to the file.
4. Append the json for big_chunk formatted appropriately to the file.
5. Append \n} to the file.

The idea is to do the json formatting out the "container" object by hand, and using your json formatter as appropriate to each of the contained objects.

CodePudding user response：

Consider a different file format, interleaving keys and values as distinct documents concatenated together within a single file:

{"next_item": "meta_data"}
{
  "description": "human-readable content goes here",
  "split over": "several lines"
}
{"next_item": "actual_data"}
["big","machine-readable","unformatted","content","here","....."]

That way you can pass any indent parameters you want to each write, and you aren't doing any serialization by hand.

See How do I use the 'json' module to read in one JSON object at a time? for how one would read a file in this format. One of its answers wisely suggests the ijson library, which accepts a multiple_values=True argument.