parse ldjson

ldparse.py

#!/usr/bin/python
import sys
import json

"""
  cat ldjson-thing | ldjson msg,time 
"""

def pick(row, path, label = ''):
    if len(path) == 1:
        [name] = path
        return (label + name), row.get(name, 'No field named %s' % name)

    name = path[0]
    return pick(row.get(name, {}), path[1:], label + name + '.')


if len(sys.argv) < 2:
    print "Include an expr!"
    sys.exit(1)

suppress_err = (len(sys.argv) == 3) and (sys.argv[2] == '-q')

expr = sys.argv[1]
projections = [path.split('.') for path in expr.split(',')]

for line in sys.stdin:
    try:
        js = json.loads(line)
        picked = [pick(js, path) for path in projections]
        print ' '.join(['%s: %s' % (name, value) for (name, value) in picked])
    except:
        if not suppress_err:
            sys.stderr.write("Failed to parse: %s" % line)