code: def nnz_obs_names(self):
          
          # nz_names = []
          # for w,n in zip(self.observation_data.weight,
          #                self.observation_data.obsnme):
          #     if w > 0.0:
          #         nz_names.append(n)
          obs = self.observation_data
  
          nz_names = list(obs.loc[obs.weight>0.0,"obsnme"])
          return nz_names
docs: get the non-zero weight observation names
  
          Returns
          -------
          nnz_obs_names : list
              a list of non-zero weighted observation names