code: def _add_timer(self, timer):
      if timer not in self._timers:
          self._timers.append(timer)
  
imports: from __future__ import division
  import atexit
  from time import sleep
  from ..base import BaseApplicationBackend, BaseCanvasBackend, BaseTimerBackend
  from ...util.ptime import time
  from ...None import config
label_desc: Use image node_id 2 for calling the ApplicationBackend obj's underlying member method code with example usage: obj._add_timer(timer) without return types