code: def optimizer_step(
      self,
      epoch_nb,
      batch_nb,
      optimizer,
      optimizer_i,
      opt_closure,
      **kwargs,
  ):
      optimizer.step()
      optimizer.zero_grad()
  
imports: import argparse
  import copy
  from argparse import Namespace
  import torch
  from experiments.ssl_experiments.pimodel_cifar10 import PIModel
  from torch import nn
  from torch.hub import load_state_dict_from_url
  from torch.utils.data import DataLoader
  from torchvision.datasets import CIFAR10
  from torchvision.models import vgg16
  from baal import ActiveLearningDataset, get_heuristic
  from baal.bayesian.dropout import patch_module
  from baal import ActiveLightningModule, BaalTrainer, ResetCallback
label_desc: Use image node_id 4 for calling the PIActiveLearningModel obj's underlying member method code with example usage: obj.optimizer_step(epoch_nb, batch_nb, optimizer, optimizer_i, opt_closure) without return types