docstr: log the time of some heavy callbacks 
docstr_tok: ["log","the","time","of","some","heavy","callbacks"]
code: def log(self):
      """log the time of some heavy callbacks"""
      if self.tot < 2:
          return
      msgs = []
      for name, t in self.times:
          if t / self.tot > 0.3 and t > 1:
              msgs.append(name + ": " + humanize_time_delta(t))
      logger.info(
          "Callbacks took {:.3f} sec in total. {}".format(
              self.tot, "; ".join(msgs)
          )
      )
  
imports: import traceback
  from contextlib import contextmanager
  from time import perf_counter
  from ..compat import tfv1
  from ..utils import logger
  from ..utils.utils import humanize_time_delta
  from .base import Callback
  from .hooks import CallbackToHook
label_desc: Use image node_id 4 for calling the CallbackTimeLogger obj's underlying member method code with example usage: obj.log() without return types