code: def show_backref(target, max_depth=3):
      """Returns a dot graph of all the objects that are referencing the target.
  
      A object referencing graph is useful to debug memory leak like circular
      reference. objgraph provides a good visualization of the memory graph than
      most python built-in utilities like gc.get_referrers(), which are not
      human-readable sometimes.
  
      The dot graph will be written to a string IO object, and can be rendered with
      graphviz in operating system.
      E.g. dot -Tpng {$dot_graph} -o output.png
      Args:
        target: The target object for the memory graph.
        max_depth: The maximum depth of the graph. By default 3 layers of references
          are used. Increases this a lot may result in the graph growing too big.
  
      Returns:
        A string that contains the object reference graph.
      Raises:
        NotImplementedError: if objgraph is not installed.
      """
      if objgraph is None:
          raise NotImplementedError("objgraph is not installed.")
      string_io = io.StringIO()
      objgraph.show_backrefs(
          target, max_depth=max_depth, output=string_io
      )
      graph = string_io.getvalue()
      string_io.close()
      return graph
  
imports: import collections
  import dataclasses
  import functools
  import io
  import itertools
  import threading
  from absl import app
  from tensorflow.python.compat import v2_compat
  from tensorflow.python.distribute import collective_all_reduce_strategy
  from tensorflow.python.distribute import multi_process_runner
  from tensorflow.python.distribute import multi_worker_test_base
  from tensorflow.python.distribute import tpu_strategy
  from tensorflow.python.distribute import values
  from tensorflow.python.eager import context
  from tensorflow.python.framework import config
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import array_ops_stack
  from tensorflow.python.util import nest
label_desc: Use image node_id 13 for calling a global function with example usage: show_backref(target, max_depth) and returns: graph