import os, signal, threading

class WatchDog():
    def __init__(self, timeout=5):
        self.timeout = timeout
        self._t = None

    def do_expire(self):
        hostname = "8.8.8.8"
        response = os.system("ping -c 1 " + hostname)
        if response == 0:
            self.refresh()
        else:
            print("Pinging 8.8.8.8 yielded no response!")
            hostname = "8.8.4.4"
            response = os.system("ping -c 1 " + hostname)
            if response == 0:
                self.refresh()
            else:
                print("Pinging 8.8.4.4 yielded no response!")

    def _expire(self):
        print("\nWatchdog expire")
        self.do_expire()

    def start(self):
        if self._t is None:
            self._t = threading.Timer(self.timeout, self._expire)
            self._t.start()

    def stop(self):
        if self._t is not None:
            self._t.cancel()
            self._t = None

    def refresh(self):
        if self._t is not None:
             self.stop()
             self.start()

wd = WatchDog()
wd.start()