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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 get_info(self, sm_id):
 """ Extract a CompositionInfo instance containing the single model of index `sm_id`. """

        sm = self.source_models[sm_id]
        num_samples = sm.samples if self.num_samples else 0
        return self.__class__(
            self.gsim_lt, self.seed, num_samples, [sm], self.tot_weight)