code: def anonymized_formula(self):
          
          anon_formula = super().anonymized_formula
          chg = self._charge
          chg_str = ""
          if chg > 0:
              chg_str += ("{}{}".format('+', str(int(chg))))
          elif chg < 0:
              chg_str += ("{}{}".format('-', str(int(np.abs(chg)))))
          return anon_formula + chg_str
docs: An anonymized formula. Appends charge to the end
          of anonymized composition