class_docstr: Optimizer hook for distributed training.
class_docstr_tok: ["Optimizer","hook","for","distributed","training","."]
code: def before_run(self, runner):
      runner.optimizer.zero_grad()
  
imports: from mmcv.runner import OptimizerHook, HOOKS
label_desc: Use image node_id 2 for calling the DistOptimizerHook obj's underlying member method code with example usage: obj.before_run(runner) without return types