code: def available_keywords():
      """
      returns a list of all possible keywords defined in the parsers
      (duplicates from sections are removed.)
      """
      all_key_parser = argparse.ArgumentParser(
          parents=[],
          description=__doc__,
          formatter_class=argparse.RawDescriptionHelpFormatter,
          conflict_handler="resolve",
      )
  
      for _, add_args_func in SUPPORTED_DEFAULT_SECTIONS.items():
          all_key_parser = add_args_func(all_key_parser)
  
      all_key_parser = add_input_data_args(all_key_parser)
  
      # add keys from custom sections
      for _, add_args_func in SUPPORTED_ARG_SECTIONS.items():
          all_key_parser = add_args_func(all_key_parser)
  
      default_keys = []
      for action in all_key_parser._actions:
          try:
              default_keys.append(action.option_strings[0][2:])
          except (IndexError, AttributeError, ValueError):
              pass
      # remove duplicates
      default_keys = list(set(default_keys))
      # remove bad names
      default_keys = [keyword for keyword in default_keys if keyword]
      return default_keys
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import argparse
  import os
  import textwrap
  from niftynet.engine.signal import TRAIN, INFER, EVAL
  from niftynet.utilities.util_common import look_up_operations
  from niftynet.engine.application_factory import ApplicationFactory
  from niftynet.engine.application_factory import SUPPORTED_APP
  from niftynet.io.misc_io import resolve_file_name
  from niftynet.utilities.niftynet_global_config import NiftyNetGlobalConfig
  from niftynet.utilities import NiftyNetLaunchConfig
  from niftynet.utilities.user_parameters_custom import SUPPORTED_ARG_SECTIONS
  from niftynet.utilities.user_parameters_custom import add_customised_args
  from niftynet.utilities.user_parameters_default import SUPPORTED_DEFAULT_SECTIONS
  from niftynet.utilities.user_parameters_default import add_input_data_args
  from niftynet.utilities.user_parameters_helper import has_section_in_config
  from niftynet.utilities.user_parameters_helper import standardise_section_name
  from niftynet.utilities.util_common import damerau_levenshtein_distance
  from niftynet.utilities.versioning import get_niftynet_version_string
label_desc: Use image node_id 1 for calling a global function with example usage: available_keywords() and returns: default_keys