code: def _get_modifiable_indices(self, current_text):
      """Returns the word indices in current_text which are able to be
      deleted."""
      try:
          return (
              set(range(len(current_text.words)))
              - current_text.attack_attrs["modified_indices"]
          )
      except KeyError:
          raise KeyError(
              "`modified_indices` in attack_attrs required for RepeatModification constraint."
          )
  
imports: from textattack.constraints import PreTransformationConstraint
label_desc: Use image node_id 1 for calling the RepeatModification obj's underlying member method code with example usage: obj._get_modifiable_indices(current_text) and returns: unknown