code: def avg_perturbation_perc(self):
      self.perturbed_word_percentages = self.perturbed_word_percentages[
          self.perturbed_word_percentages > 0
      ]
      average_perc_words_perturbed = (
          self.perturbed_word_percentages.mean()
      )
      average_perc_words_perturbed = round(
          average_perc_words_perturbed, 2
      )
      return average_perc_words_perturbed
  
file_path: TextAttack/textattack/metrics/attack_metrics/words_perturbed.py
imports: import numpy
  from textattack.attack_results import FailedAttackResult, SkippedAttackResult
  from textattack.metrics import Metric
label_desc: Use image node_id 4 for calling the WordsPerturbed obj's underlying member method code with example usage: obj.avg_perturbation_perc() and returns: average_perc_words_perturbed