def zGetSurfaceData(self, surfNum):
        """Return surface data"""
        if self.pMode == 0: # Sequential mode
            surf_data = _co.namedtuple('surface_data', ['radius', 'thick', 'material', 'semidia', 
                                                        'conic', 'comment'])
            surf = self.pLDE.GetSurfaceAt(surfNum)
            return surf_data(surf.pRadius, surf.pThickness, surf.pMaterial, surf.pSemiDiameter,
                             surf.pConic, surf.pComment)
        else:
            raise NotImplementedError('Function not implemented for non-sequential mode')
Return surface data