code: def peirce_skill_score(self):
          
          n = float(self.table.sum())
          nf = self.table.sum(axis=1)
          no = self.table.sum(axis=0)
          correct = float(self.table.trace())
          return (correct / n - (nf * no).sum() / n ** 2) / (1 - (no * no).sum() / n ** 2)
docs: Multiclass Peirce Skill Score (also Hanssen and Kuipers score, True Skill Score)