class_docstr: Base class for callbacks that can be registered with type :class:`BaseTrainer`
  
  Attr:
      config(omegaconf.DictConfig): Config for the callback
      trainer(Type[BaseTrainer]): Trainer object
class_docstr_tok: ["Base","class","for","callbacks","that","can","be","registered","with","type",":","class",":","`","BaseTrainer","`","Attr",":","config","(","omegaconf.DictConfig",")",":","Config","for","the","callback","trainer","(","Type","[","BaseTrainer","]",")",":","Trainer","object"]
docstr: Called before each train update.
docstr_tok: ["Called","before","each","train","update","."]
code: def on_update_start(self, **kwargs) -> None:
      """
      Called before each train update.
      """
      pass
  
imports: from typing import Type
  from mmf.trainers.base_trainer import BaseTrainer
  from omegaconf import DictConfig
label_desc: Use image node_id 9 for calling the Callback obj's underlying member method code with example usage: obj.on_update_start() without return types