code: def __len__(self):
      return self.total_sequences
  
imports: import json
  import math
  import numpy
  import torch
  from megatron import get_args
  from megatron import print_rank_0
  from megatron import get_tokenizer
  from .detokenizer import get_detokenizer
label_desc: Use image node_id 2 for calling the _LMDataset obj's underlying member method code with example usage: obj.__len__() and returns: self