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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 nonzero(self):
 """ property decorated method to get a new ObservationEnsemble of only non-zero weighted observations Returns ------- ObservationEnsemble : ObservationEnsemble """

        df = self.loc[:,self.pst.nnz_obs_names]
        return ObservationEnsemble.from_dataframe(df=df,
                        pst=self.pst.get(obs_names=self.pst.nnz_obs_names))