code: def __getitem__(self, idx):
      input_ids = self.indexed_dataset[idx]["input_ids"]
      seq_boundaries = self.indexed_dataset[idx]["seq_start_id"] + [
          len(input_ids)
      ]
      loss_mask = self.indexed_dataset[idx]["loss_mask"]
      return {
          "input_ids": input_ids,
          "seq_boundaries": seq_boundaries,
          "loss_mask": loss_mask,
      }
  
imports: import re
  from typing import List, Mapping, Optional
  import datasets
  import numpy
  import torch
  from datasets import load_dataset
  from nemo.collections.common.tokenizers.tokenizer_spec import TokenizerSpec
  from nemo.collections.nlp.data.language_modeling.megatron.dataset_utils import get_samples_mapping
  from nemo.collections.nlp.data.language_modeling.text_memmap_dataset import JSONLMemMapDataset
  from nemo.core.classes import Dataset
  from nemo.utils import logging
label_desc: Use image node_id 2 for calling the GPTSFTPackedDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: dict