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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def nnz_obs_names(self):
 """ wrapper around pyemu.Pst.nnz_obs_names for listing non-zero observation names Returns ------- nnz_obs_names : list pyemu.Pst.nnz_obs_names """

        if self.__pst is not None:
            return self.pst.nnz_obs_names
        else:
            return self.jco.obs_names