code: def make_ref_shard_files(out_dir):
      tf.gfile.MakeDirs(out_dir)
      opts = tf.python_io.TFRecordOptions(
          tf.python_io.TFRecordCompressionType.GZIP
      )
      files = [
          tf.python_io.TFRecordWriter(
              os.path.join(out_dir, REF_SHARD_FILE % i), opts
          )
          for i in range(cc_utils.NUM_SHARDS)
      ]
      return files
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import json
  import math
  import os
  import re
  import string
  import tempfile
  import six
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.data_generators import tokenizer
  from tensor2tensor.data_generators.wikisum import utils
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import metrics
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
label_desc: Use image node_id 1 for calling a global function with example usage: make_ref_shard_files(out_dir) and returns: files