code: def constant_tuple_dict(self):
          
          return {constant_tuple.constant: constant_tuple
                  for name, prior_model in self.prior_model_tuples
                  for constant_tuple in prior_model.constant_tuples}.values()
docs: Returns
          -------
          constant_tuple_dict: {Constant: ConstantTuple}
              The set of all constants associated with this mapper