old_contents: from menpo.fit.lucaskanade.residual import SSD
  from menpo.fit.lucaskanade.base import LucasKanade
  
  
  class AppearanceLucasKanade(LucasKanade):
  
      def __init__(self, model, transform, eps=10**-6):
          super(AppearanceLucasKanade, self).__init__(SSD(), transform, eps=eps)
  
          # in appearance alignment, target image is aligned to appearance model
          self.appearance_model = model
          # by default, template is assigned to mean appearance
          self.template = model.mean
          # pre-compute
          self._set_up()
  
new_contents: from menpo.fit.lucaskanade.residual import SSD
  from menpo.fit.lucaskanade.base import LucasKanade
  
  
  class AppearanceLucasKanade(LucasKanade):
  
      def __init__(self, model, transform, eps=10**-6):
          # note that the only supported residual for Appearance LK is SSD.
          # this is becuase in general we don't know to take the approprate
          # derivatives for arbitrary resiudals with (for instance) a project out
          # AAM. 
          # see https://github.com/menpo/menpo/issues/130 for details.
          super(AppearanceLucasKanade, self).__init__(SSD(), transform, eps=eps)
  
          # in appearance alignment, target image is aligned to appearance model
          self.appearance_model = model
          # by default, template is assigned to mean appearance
          self.template = model.mean
          # pre-compute
          self._set_up()
  
subject: Update base.py