code: def list_files(suffix=""):
      """
      Returns a list of all files in CleverHans with the given suffix.
  
      Parameters
      ----------
      suffix : str
  
      Returns
      -------
  
      file_list : list
          A list of all files in CleverHans whose filepath ends with `suffix`.
      """
  
      cleverhans_path = os.path.abspath(cleverhans.__path__[0])
      # In some environments cleverhans_path does not point to a real directory.
      # In such case return empty list.
      if not os.path.isdir(cleverhans_path):
          return []
      repo_path = os.path.abspath(
          os.path.join(cleverhans_path, os.pardir)
      )
      file_list = _list_files(cleverhans_path, suffix)
  
      extra_dirs = [
          "cleverhans_tutorials",
          "examples",
          "scripts",
          "tests_tf",
          "tests_pytorch",
      ]
  
      for extra_dir in extra_dirs:
          extra_path = os.path.join(repo_path, extra_dir)
          if os.path.isdir(extra_path):
              extra_files = _list_files(extra_path, suffix)
              extra_files = [
                  os.path.join(os.pardir, path) for path in extra_files
              ]
              file_list = file_list + extra_files
  
      return file_list
  
label_desc: Use image node_id 1 for calling a global function with example usage: list_files(suffix) and returns: file_list, list