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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, mf_id):
 """ Retreive model fitting with identifier 'mf_id' from the list of model fitting objects stored in self.model_fitting """

        for model_fitting in self.model_fittings:
            if model_fitting.activity.id == mf_id:
                return model_fitting

        raise Exception("Model fitting activity with id: " + str(mf_id) +
                        " not found.")