class_docstr: Base class to perform model training.
  
  Args:
      model (BaseAE): A instance of :class:`~pythae.models.BaseAE` to train
  
      train_dataset (BaseDataset): The training dataset of type
          :class:`~pythae.data.dataset.BaseDataset`
  
      eval_dataset (BaseDataset): The evaluation dataset of type
          :class:`~pythae.data.dataset.BaseDataset`
  
      training_config (BaseTrainerConfig): The training arguments summarizing the main
          parameters used for training. If None, a basic training instance of
          :class:`BaseTrainerConfig` is used. Default: None.
  
      callbacks (List[~pythae.trainers.training_callbacks.TrainingCallbacks]):
          A list of callbacks to use during training.
code: def _optimizers_step(self, model_output=None):
      loss = model_output.loss
  
      self.optimizer.zero_grad()
      loss.backward()
      self.optimizer.step()
  
imports: import contextlib
  import datetime
  import logging
  import os
  from copy import deepcopy
  from typing import Any, Dict, List, Optional, Union
  import torch
  import torch.distributed
  import torch.optim
  import torch.optim.lr_scheduler
  from torch.nn.parallel import DistributedDataParallel
  from torch.utils.data import DataLoader, Dataset
  from torch.utils.data.distributed import DistributedSampler
  from ...customexception import ModelError
  from ...data.datasets import BaseDataset, collate_dataset_output
  from ...models import BaseAE
  from ..trainer_utils import set_seed
  from ..training_callbacks import CallbackHandler, MetricConsolePrinterCallback, ProgressBarCallback, TrainingCallback
  from .base_training_config import BaseTrainerConfig
label_desc: Use image node_id 14 for calling the BaseTrainer obj's underlying member method code with example usage: obj._optimizers_step(model_output) without return types