class_docstr: This class represents a dataset for fine-tuning GPT models using the Megatron framework.
  
  Args:
      name (str): Name of the dataset equals to data_prefix
  
      indexed_dataset (IndexedDataset): The dataset object containing the data samples.
  
      max_seq_length (int): Maximum sequence length for each sample in the dataset.
  
      fewshot_list (list): A list of few-shot learning examples, if applicable.
code: def __len__(self):
      return len(list(self.indexed_dataset))
  
imports: import json
  import torch
  import numpy
  import glob
  from collections import OrderedDict
  from megatron import get_tokenizer, get_args, get_retro_args
label_desc: Use image node_id 2 for calling the FtDataset obj's underlying member method code with example usage: obj.__len__() and returns: len