Returns a single field from a json textfile - The example I use has the format {"msg":{"key":"value",...}}

jsonread.py

#Usage: jsonread.py <json_filename> <field>

import json
import sys  #just for arguments
from pprint import pprint

with open(sys.argv[1]) as data_file:
    data=json.loads(data_file.read())
    
    pprint(data['msg'][sys.argv[2]])