code: def _initialize_optimizer_and_scheduler(
      self, optimizer, scheduler, num_epochs, sub_train, base_lr
  ):
      steps = (len(sub_train) // self.mini_batch_size) + int(
          len(sub_train) % self.mini_batch_size != 0
      )
  
      if optimizer is None:
          params, optimizer = (
              self._default_optimizer(base_lr)
              if optimizer is None
              else optimizer
          )
  
      if scheduler == "linear":
          try:
              from transformers import get_linear_schedule_with_warmup
  
              scheduler = get_linear_schedule_with_warmup(
                  optimizer,
                  num_warmup_steps=0,
                  num_training_steps=steps * num_epochs,
              )
          except ImportError:
              raise ValueError(
                  "Linear scheduler is only available when the transformers "
                  "integration is installed "
              )
  
      elif scheduler is None:
          # constant learning rate
          scheduler = LambdaLR(optimizer, lambda _: 1)
      elif not isinstance(scheduler, _LRScheduler):
          raise ValueError(f"Invalid scheduler: {scheduler}")
  
      return optimizer, scheduler
  
imports: import logging
  import warnings
  from abc import abstractmethod
  from functools import partial
  from pathlib import Path
  from small_text.classifiers.classification import Classifier
  from small_text.integrations.pytorch.exceptions import PytorchNotFoundError
  from small_text.training.early_stopping import EarlyStopping, NoopEarlyStopping, EarlyStoppingOrCondition
  from small_text.training.metrics import Metric
  from small_text.training.model_selection import ModelSelection, NoopModelSelection
  from small_text.utils.classification import empty_result, prediction_result
label_desc: Use image node_id 11 for calling the PytorchClassifier obj's underlying member method code with example usage: obj._initialize_optimizer_and_scheduler(optimizer, scheduler, num_epochs, sub_train, base_lr) and returns: optimizer,  scheduler