code: def __len__(self):
      return sum(len(itr) for itr in self.itr)
  
imports: from collections import OrderedDict
  import numpy
  from fairseq.data import BaseWrapperDataset, FairseqDataset, iterators
label_desc: Use image node_id 2 for calling the MultiItr obj's underlying member method code with example usage: obj.__len__() and returns: sum