class_docstr: Estimate the time left until completion of training.
code: def _before_train(self):
      self._max_epoch = self.trainer.max_epoch
      self._last_time = time.time()
  
imports: import numpy
  import os
  import time
  from collections import deque
  from ..utils import logger
  from ..utils.utils import humanize_time_delta
  from .base import Callback
label_desc: Use image node_id 2 for calling the EstimatedTimeLeft obj's underlying member method code with example usage: obj._before_train() without return types