code: def average(self, start_index=0):
      ret = {}
      for key, times in self.results.items():
          ret[key] = {
              "time": np.mean(times[start_index:]) * (10**3),
              "num": len(times) - start_index,
              "scale": "ms",
          }
  
      return ret
  
imports: from __future__ import absolute_import
  import csv
  import os
  import time
  from collections import OrderedDict
  from contextlib import contextmanager
  from importlib import import_module
  import numpy
  from nnabla.ext_utils import import_extension_module
  from .base import FunctionHookCallbackBase
label_desc: Use image node_id 6 for calling the CpuTimerCallback obj's underlying member method code with example usage: obj.average(start_index) and returns: ret