class_docstr: Callback for handling train/validation logistics, report summarization,
  logging etc.
class_docstr_tok: ["Callback","for","handling","train\/validation","logistics",",","report","summarization",",","logging","etc","."]
code: def on_train_start(self):
      self.train_timer = Timer()
      self.snapshot_timer = Timer()
  
file_path: mmf/mmf/trainers/callbacks/logistics.py
imports: import logging
  import torch
  from mmf.trainers.callbacks.base import Callback
  from mmf.utils.configuration import get_mmf_env
  from mmf.utils.logger import calculate_time_left, setup_output_folder, summarize_report, TensorboardLogger, WandbLogger
  from mmf.utils.timer import Timer
label_desc: Use image node_id 2 for calling the LogisticsCallback obj's underlying member method code with example usage: obj.on_train_start() without return types