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