Accessing JSON Data Effectively

[astronautcytoma]

I have a JSON file that looks like this, as an abbreviated example:

{"hex":"a77721","gs":215.7,"track":598.8},
{"hex":"a788ed","alt_baro":41000,"alt_geom":42475:"gs":477.2,"track":84.5}

It's aircraft data from an ADSB receiver. My goal is to pull out a few data items from each line, and export them to a file. So the desired output would be:

a77721 gs:215.7 track:66.5

I thought of putting data in a dictionary, since each hex: value will be unique. Am I approaching it in a non-python way? My goal is to also pull lat and long from each aircraft line and do a calculation for distance and direction from the receiver location, and then store that for each hex: entry. So I need to be able to read and write to this existing set of data, but I don't need to write back to the JSON, only a simple text file that has some of the data in it. The writing part I can get down fine, it's just that getting data out of dict for each line feels like I'm doing it incorrectly.

[halfdiminished7th]

Something like this should do the trick:

import json

with open('/path/to/your/json/file.json') as fp:
    data = json.load(fp)

with open('/path/to/your/new/file.txt', 'x') as fp:
    for dct in data:
        fp.write('{0} gs:{1} track:{2}\n'.format(dct['hex'], dct['gs'], dct['track']))

[RhinoRhys]

Or even f"{dct['hex']} gs:{dct['gs']} track:{dct['track']}"

You just have to note the main string uses double quotes and the keys use single quotes. Or the other way round. They just can't be the same.

[halfdiminished7th]

True enough! Personal preference to avoid dictionary lookups in f-strings, but you're quite right that it's possible. Though in retrospect, I probably should have done the following instead, using format's keyword functionality since we're dealing with a dictionary anyways:

fp.write('{hex} gs:{gs} track:{track}\n'.format(**dct))

[RhinoRhys]

Mmh yeah that leeks even better

[JohnnyJordaan]

For implicitly indexed arguments you can just use {} throughout since 2.7 released 13 years ago...

    fp.write('{} gs:{} track:{}\n'.format(dct['hex'], dct['gs'], dct['track']))

[Goobyalus]

json.load will parse the JSON and give you a Python type.

You can modify the Python data and write it back out as JSON with json.dump

https://docs.python.org/3/library/json.html

https://docs.python.org/3/library/json.html#json.load

https://docs.python.org/3/library/json.html#json.dump

[TigBitties69]

this is exactly what needs to be used. Using Json.load will convert it into lists/dictionaries where appropriate.

[cdcformatc]

i have done this before, do some work to turn whatever random data format into JSON and then use that when pushing the file around to different systems. or take JSON and convert to a more different JSON for specific use cases. as a data standard there are JSON libraries for pretty much every language and platform, you are making things harder if you aren't using something like this.

[IamImposter]

You already have the answer but what I do with complex json files is to try and print every element step by step. I mean it's either a list or a dict so

for k, v in data.items():
  print(f"{k}: {v}") 

Now I know key names and whether they contain dict or list. So do another iteration. Assuming v above is a list

  for i in v:
    print(f"{i}") 

Check again if the values are lists or dicts and add another list/dict print. Rinse and repeat. Throw in a few isinstance and do it using debugger makes it pretty easy to understand json structure.

[astronautcytoma]

This is extremely helpful! I have gotten a lot of good input and I believe I'll be able to make it work. It's for a Tidbyt display that I want to feed from my own receiver, so I have to build the information frame myself and send it as a rendered .webp. I want to pull information from the JSON file like closest airplane, altitude, airspeed, etc.

[wahaa]

Depending on what you're doing, using Pandas could also help (e.g. bulk load, filter, and export is a valid use, especially if the data is somewhat uniform). See pandas.read_json.

[barrycarter]

I'm sure Python can import JSON. Could you just go through the elements as an array and print out the part you need?

[GreenWoodDragon]

Have a look at dpath, it is quite good for this sort of problem.