code: def help_string():
      """Generate help string with contents of registry."""
      help_str = """
  Registry contents:
  ------------------
  
    Models:
  %s
  
    HParams:
  %s
  
    RangedHParams:
  %s
  
    Problems:
  %s
  
    Optimizers:
  %s
  
    Attacks:
  %s
  
    Attack HParams:
  %s
  
    Pruning HParams:
  %s
  
    Pruning Strategies:
  %s
  
    Env Problems:
  %s
  """
      lists = tuple(
          display_list_by_prefix(entries, starting_spaces=4)
          for entries in [  # pylint: disable=g-complex-comprehension
              list_models(),
              list_hparams(),
              list_ranged_hparams(),
              list_base_problems(),
              list_optimizers(),
              list_attacks(),
              list_attack_params(),
              list_pruning_params(),
              list_pruning_strategies(),
              list_env_problems(),
          ]
      )
      return help_str % lists
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  from tensor2tensor.utils import misc_utils
  import tensorflow.compat.v1
  from tensorflow.python.util import tf_inspect
label_desc: Use image node_id 15 for calling a global function with example usage: help_string() and returns: unknown