code: def start(self) -> None:
          
          # Looking up the IOLoop here allows to first instantiate the
          # PeriodicCallback in another thread, then start it using
          # IOLoop.add_callback().
          self.io_loop = IOLoop.current()
          self._running = True
          self._next_timeout = self.io_loop.time()
          self._schedule_next()
docs: Starts the timer.