code: def _expand(self, normalization, csphase, **kwargs):
          
          if normalization.lower() == '4pi':
              norm = 1
          elif normalization.lower() == 'schmidt':
              norm = 2
          elif normalization.lower() == 'unnorm':
              norm = 3
          elif normalization.lower() == 'ortho':
              norm = 4
          else:
              raise ValueError(
                  "The normalization must be '4pi', 'ortho', 'schmidt', " +
                  "or 'unnorm'. Input value was {:s}."
                  .format(repr(normalization))
                  )
  
          cilm = _shtools.SHExpandDH(self.data, norm=norm, csphase=csphase,
                                     sampling=self.sampling,
                                     **kwargs)
          coeffs = SHCoeffs.from_array(cilm,
                                       normalization=normalization.lower(),
                                       csphase=csphase, copy=False)
          return coeffs
docs: Expand the grid into real spherical harmonics.