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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 combine_duplicates(self):
 """Combine duplicates among `stmts` and save result in `unique_stmts`. A wrapper around the static method :py:meth:`combine_duplicate_stmts`. """

        if self.unique_stmts is None:
            self.unique_stmts = self.combine_duplicate_stmts(self.stmts)
        return self.unique_stmts