code: def fit(self, data):
      return DiffusionSpectrumFit(self, data)
  
imports: import numpy
  from scipy.ndimage import map_coordinates
  from scipy.fftpack import fftn, fftshift, ifftshift
  from dipy.reconst.odf import OdfModel, OdfFit
  from dipy.reconst.cache import Cache
  from dipy.reconst.multi_voxel import multi_voxel_fit
label_desc: Use image node_id 2 for calling the DiffusionSpectrumModel obj's underlying member method code with example usage: obj.fit(data) and returns: DiffusionSpectrumFit