munin.conf

contacts pushover
contact.pushover.command /path/to/pushover_munin.py

pushover_munin.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
import urllib2
from urllib import urlencode

APPTOKEN = YOUR_APPLICATION_TOKEN
USERTOKEN = YOUR_USER_TOKEN


def main():
    message = sys.stdin.read()

    params = dict(
        token=APPTOKEN,
        user=USERTOKEN,
        message=message)
    request = urllib2.Request(url='https://api.pushover.net/1/messages.json',
                            data=urlencode(params))
    urllib2.urlopen(request)
    return 0


if __name__ == u'__main__':
    sys.exit(main())