Ionic radius of specie. Returns None if data is not present.

def ionic_radius(self):
        """
        Ionic radius of specie. Returns None if data is not present.
        """

        if self._oxi_state in self.ionic_radii:
            return self.ionic_radii[self._oxi_state]
        d = self._el.data
        oxstr = str(int(self._oxi_state))
        if oxstr in d.get("Ionic radii hs", {}):
            warnings.warn("No default ionic radius for %s. Using hs data." %
                          self)
            return d["Ionic radii hs"][oxstr]
        elif oxstr in d.get("Ionic radii ls", {}):
            warnings.warn("No default ionic radius for %s. Using ls data." %
                          self)
            return d["Ionic radii ls"][oxstr]
        warnings.warn("No ionic radius for {}!".format(self))
        return None