class_docstr: MNIST, tuning data.
code: def generator(self, data_dir, tmp_dir, is_training):
      if is_training:
          return mnist_generator(tmp_dir, True, 55000)
      else:
          return mnist_generator(tmp_dir, True, 5000, 55000)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import gzip
  import os
  import random
  import numpy
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import image_utils
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
label_desc: Use image node_id 7 for calling the ImageMnistTune obj's underlying member method code with example usage: obj.generator(data_dir, tmp_dir, is_training) and returns: mnist_generator, mnist_generator