How to set the extrapolation strategy

[XDXM147]

Hello, when I use this function, if the result falls outside the domain, is the extrapolation result defaulted to returning NaN? I hope to set this extrapolation strategy to a specific numerical value. How do I modify it? I have tried to modify the _interpret_t(self, t) function, but it makes the speed very slow. I hope you can help me solve this problem, thank you very much.