class_docstr: This class implements several methods to keep track of intermediate
  variables.
  
  This is useful for eg. visualizing or retrieving gradients wrt. inputs
  later on
class_docstr_tok: ["This","class","implements","several","methods","to","keep","track","of","intermediate","variables",".","This","is","useful","for","eg",".","visualizing","or","retrieving","gradients","wrt",".","inputs","later","on"]
code: def __getitem__(self, name):
      return self.tracker[name]
  
imports: import abc
  import math
  import torch
  import torch.nn
  import torch.nn.functional
  from fairseq import utils
  from fairseq.models import FairseqIncrementalDecoder, transformer
  from pytorch_translate import rnn_cell, utils, vocab_reduction
  from pytorch_translate.research.lexical_choice import lexical_translation
label_desc: Use image node_id 4 for calling the VariableTracker obj's underlying member method code with example usage: obj.__getitem__(name) and returns: self