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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_model_fitting(self, con_est_id):
 """ Retreive model fitting that corresponds to contrast with identifier 'con_id' from the list of model fitting objects stored in self.model_fittings """

        for (mpe_id, pe_ids), contrasts in self.contrasts.items():
            for contrast in contrasts:
                if contrast.estimation.id == con_est_id:
                    model_fitting_id = mpe_id
                    pe_map_ids = pe_ids
                    break

        for model_fitting in self.model_fittings:
            if model_fitting.activity.id == model_fitting_id:
                return (model_fitting, pe_map_ids)

        raise Exception("Model fitting of contrast : " + str(con_est_id) +
                        " not found.")