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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 to_df(self, method: str = 'MEMORY', **kwargs) -> 'pd.DataFrame': """ Export this SAS Data Set to a Pandas Data Frame :param method: defaults to MEMORY; the original method. CSV is the other choice which uses an intermediary csv file; faster for large data :param kwargs: :return: Pandas data frame """

        ll = self._is_valid()
        if ll:
            print(ll['LOG'])
            return None
        else:
            return self.sas.sasdata2dataframe(self.table, self.libref, self.dsopts, method, **kwargs)