code: def __next__(self):
      self.step += 1
      if self.step % 2 == 0:
          data = next(self.iterator_head)
      else:
          data = next(self.iterator_tail)
      return data
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  import torch
  from torch.utils.data import Dataset
label_desc: Use image node_id 2 for calling the BidirectionalOneShotIterator obj's underlying member method code with example usage: obj.__next__() and returns: data