class_docstr: Dataset of images built from a list of paths to zip files.
  
  This dataset reads an external image file in given zipfiles. The
  zipfiles shall contain only image files.
  This shall be able to replace ImageDataset and works better on NFS
  and other networked file systems. The user shall find good balance
  between zipfile size and number of zipfiles (e.g. granularity)
  
  Args:
      zipfilenames (list of strings): List of zipped archive filename.
      dtype: Data type of resulting image arrays. ``chainer.config.dtype`` is
          used by default (see :ref:`configuration`).
code: def __len__(self):
      return self._zpaths_accumlens[-1]
  
imports: import bisect
  import io
  import os
  import threading
  import zipfile
  import numpy
  import six
  import chainer
  from chainer.dataset import dataset_mixin
label_desc: Use image node_id 2 for calling the MultiZippedImageDataset obj's underlying member method code with example usage: obj.__len__() and returns: self