If you want to produce valid JSON file you need to write all values at once, not one value at a time (which will produce ndjson or JSON lines)

So, for a valid JSON

values = [{"first_name": "John", "last_name": "Smith", "food": "corn"},
          {"first_name": "Jane", "last_name": "Doe", "food": "soup"}]

import json
with open('some_file.json', 'w') as f:
    json.dump(values, f, indent=4)

some_file.json

[
    {
        "first_name": "John",
        "last_name": "Smith",
        "food": "corn"
    },
    {
        "first_name": "Jane",
        "last_name": "Doe",
        "food": "soup"
    }
]

if you really need ndjson - you can use ndjson package (need install via pip from PyPi).

import ndjson

with open('some_file2.ndjson', 'w') as f:
    ndjson.dump(values, f)

some_file2.ndjson

{"first_name": "John", "last_name": "Smith", "food": "corn"}
{"first_name": "Jane", "last_name": "Doe", "food": "soup"}

Alternative to ndjson package is jsonlines package