code: def _load_packed_dataset(self, file_path):
      self.indexed_dataset = np.load(file_path, allow_pickle=True)
  
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 4 for calling the GPTSFTPackedDataset obj's underlying member method code with example usage: obj._load_packed_dataset(file_path) without return types