Autoshutdown in no internet connectivity

from os import *
import urllib.request
import time

#A function for checking the connectiviy with internet.
#Return: If connection establishes, a urlopen handle otherwise None.
def testconnection():
    try:
        f = urllib.request.urlopen("http://www.google.com")
    except:
        print("NOT OK")
    else:
        print("OK")
        return f


while True:
    ff = testconnection()
#   check for the urlopen handle, if connection is not present follow this path,
    if(ff == None):
        print("No Internet Connection! Shutting Down System!")
#       works only in Windows; TODO extend for linux as well
        system("shutdown /s /t 100")
        exit(0)
#   If connection exist, then sleep for 15 minutes and loop back.
    else:
        print("InternetConnection Intact")
        time.sleep(15*60)