code: def get_feh(cls, filename):
          
          X,Y,Z = cls._get_XYZ(filename)
  
          Xsun = 0.703812
          Zsun = 0.016188
  
          return np.log10((Z/X) / (Zsun/Xsun))
docs: example filename: yapsi_w_X0p602357_Z0p027643.dat