class_docstr: Callback which executes a LR scheduler. It is executed after every
  batch iteration.
class_docstr_tok: ["Callback","which","executes","a","LR","scheduler",".","It","is","executed","after","every","batch","iteration","."]
code: def on_update_end(self, **kwargs):
      if self._scheduler is not None:
          self._scheduler.step()
  
imports: from mmf.trainers.callbacks.base import Callback
  from mmf.utils.build import build_scheduler
label_desc: Use image node_id 2 for calling the LRSchedulerCallback obj's underlying member method code with example usage: obj.on_update_end() without return types