code: def _timer_start(self):
      self._timer_stop()
      if self._single:
          ioloop = tornado.ioloop.IOLoop.instance()
          self._timer = ioloop.add_timeout(
              datetime.timedelta(milliseconds=self.interval),
              self._on_timer,
          )
      else:
          self._timer = tornado.ioloop.PeriodicCallback(
              self._on_timer, self.interval
          )
          self._timer.start()
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import six
  import datetime
  import io
  import json
  import os
  import warnings
  import numpy
  import tornado
  from matplotlib.backends import backend_agg
  from matplotlib.backend_bases import _Backend
  from matplotlib import backend_bases
  from matplotlib import _png
label_desc: Use image node_id 1 for calling the TimerTornado obj's underlying member method code with example usage: obj._timer_start() without return types