JSON stream extractor

extract_data.py

#!/usr/bin/env python

""" parses a JSON document on stdin, and prints to stdout the portion of the document
referenced by the Python getter substring given as the first argument.

This implementation uses eval(), so use with care! No warranty implied.

For example

$ curl 'http://api.duckduckgo.com/?q=ramen&format=json' 2> /dev/null | ~/bin/extract_data.py '["RelatedTopics"][0]["Text"]'
RamenA Japanese noodle soup dish.

"""

import argparse
import json
import logging
import sys

parser = argparse.ArgumentParser()
parser.add_argument('getter', help="Python object access string, e.g. ['foo']['bar'][0]")
args = parser.parse_args()

try:
    payload = json.loads(sys.stdin.read())
    value = eval('payload' + args.getter)
    result = value
    print(str(result))
except:
   logging.warning("failed to retrieve '{}' from input '{}'".format(args.getter, payload))