def printMetric():
    args = ['/var/lib/ganglia/rrds/__SummaryInfo__/cpu_system.rrd', 'AVERAGE']
rrdMetric = rrdtool.fetch(args)
time = rrdMetric[0][0]
step = rrdMetric[0][2]
sys.stdout.write('  {\n    "Key1":"' + rrdMetric[1][0] + '",\n    "Key2":"' +
    'abcd' + """",
    "metric_name":\"""" + 'cpu_system' + '",\n')
firstDP = True
sys.stdout.write('    "datapoints":[\n')
for tuple in rrdMetric[2]:
    if tuple[0] is not None:
        if not firstDP:
            sys.stdout.write(',\n')
firstDP = False
sys.stdout.write('      [')
sys.stdout.write(str(tuple[0]))
sys.stdout.write(',')
sys.stdout.write(str(time))
sys.stdout.write(']')
time = time + step
sys.stdout.write('\n    ]\n  }')
printMetric()
Convert .rrd file to json in python