code: def summarize_variables(var_list=None, tag=None):
      """Summarize the variables.
  
      Args:
        var_list: a list of variables; defaults to trainable_variables.
        tag: name scope of the summary; defaults to training_variables/.
      """
      if var_list is None:
          var_list = tf.trainable_variables()
      if tag is None:
          tag = "training_variables/"
  
      name_to_var = {v.name: v for v in var_list}
      for v_name in list(name_to_var):
          v = name_to_var[v_name]
          tf.summary.histogram(tag + v_name, v)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  from tensor2tensor.layers import common_layers
  from tensor2tensor.utils import adafactor
  from tensor2tensor.utils import contrib
  from tensor2tensor.utils import misc_utils
  from tensor2tensor.utils import mlperf_log
  from tensor2tensor.utils import multistep_optimizer
  from tensor2tensor.utils import registry
  from tensor2tensor.utils import yellowfin
  import tensorflow.compat.v1
  from tensorflow.python.framework import dtypes
label_desc: Use image node_id 15 for calling a global function with example usage: summarize_variables(var_list, tag) without return types