class_docstr: Allen Brain Atlas histology dataset.
  
  See also: http://help.brain-map.org/
  
  Notes:
  
    * 64px to 64px identity mapping problem, no in-painting.
class_docstr_tok: ["Allen","Brain","Atlas","histology","dataset",".","See","also",":","http",":","\/\/help.brain-map.org\/","Notes",":","*","64px","to","64px","identity","mapping","problem",",","no","in-painting","."]
code: def train_shards(self):
      return 100
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from io import BytesIO
  import math
  import os
  import numpy
  import requests
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import image_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import contrib
  from tensor2tensor.utils import metrics
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
label_desc: Use image node_id 1 for calling the Img2imgAllenBrain obj's underlying member method code with example usage: obj.train_shards() and returns: int