Starts running the timer.  If the timer is currently running, then
        this method will do nothing.

        :sa     stop, reset

def start(self):
        """
        Starts running the timer.  If the timer is currently running, then
        this method will do nothing.

        :sa     stop, reset
        """
        if self._timer.isActive():
            return

        self._starttime = datetime.datetime.now()
        self._timer.start()