code: def __len__(self):
      return len(self.tokens)
  
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 3 for calling the _LambadaDataset obj's underlying member method code with example usage: obj.__len__() and returns: len