code: def get_skeleton(self):
          
          src_groups = []
          for grp in self.src_groups:
              sg = copy.copy(grp)
              sg.sources = []
              src_groups.append(sg)
          return self.__class__(self.names, self.weight, self.path, src_groups,
                                self.num_gsim_paths, self.ordinal, self.samples)
docs: Return an empty copy of the source model, i.e. without sources,
          but with the proper attributes for each SourceGroup contained within.