code: def average_cationic_radius(self):
          
          if "Ionic radii" in self._data:
              radii = [v for k, v in self._data["Ionic radii"].items()
                       if int(k) > 0]
              if radii:
                  return sum(radii) / len(radii)
          return 0
docs: Average cationic radius for element (with units). The average is
          taken over all positive oxidation states of the element for which
          data is present.