code: def _train(self, *args, **kwargs):
      raise NotImplementedError
  
imports: from abc import ABC, abstractmethod
  import torch
  from nebullvm.operations.base import Operation
  from nebullvm.operations.fetch_operations.local import FetchModelFromLocal
  from torch.utils.data import DataLoader
  from torchvision import datasets
  from forward_forward.operations.data import VOCABULARY
  from forward_forward.operations.fetch_operations import FetchTrainingDataFromLocal
  from forward_forward.utils.labels import LabelsInjector
  from forward_forward.utils.modules import FCNetFFProgressive
  from forward_forward.utils.utils import ProgressiveTrainingDataset, compute_perplexity
label_desc: Use image node_id 4 for calling the BaseForwardForwardTrainer obj's underlying member method code with example usage: obj._train() without return types