test.py

#!/usr/bin/env python

import Foundation
import objc
import AppKit

class MountainLionNotification(Foundation.NSObject):

    def notify(self, title, subtitle, text, url):
        NSUserNotification = objc.lookUpClass('NSUserNotification')
        NSUserNotificationCenter = objc.lookUpClass('NSUserNotificationCenter')
        notification = NSUserNotification.alloc().init()
        notification.setTitle_(str(title))
        notification.setSubtitle_(str(subtitle))
        notification.setInformativeText_(str(text))
        notification.setSoundName_("NSUserNotificationDefaultSoundName")
        notification.setHasActionButton_(True)
        notification.setOtherButtonTitle_("View")
        notification.setUserInfo_({"action":"open_url", "value":url})
        NSUserNotificationCenter.defaultUserNotificationCenter().setDelegate_(self)
        NSUserNotificationCenter.defaultUserNotificationCenter().scheduleNotification_(notification)

    def userNotificationCenter_didActivateNotification_(self, center, notification):
        userInfo = notification.userInfo()
        if userInfo["action"] == "open_url":
            import subprocess
            subprocess.Popen(['open', userInfo["value"]])

MountainLionNotification().notify("t", "s", "text", "url")