If you want to _actually_ calculate Fibonacci numbers not use it as a (poor) benchmark for funcalls/recursive overheads or for other purposes, then you may also find this interesting: [https://sahandsaba.com/five-ways-to-calculate-fibonacci-numbers-with-python-code.html](https://sahandsaba.com/five-ways-to-calculate-fibonacci-numbers-with-python-code.html)
In terms of the closed form formula, it would be nice if someone wrapped `mpfr` or similar someday for a `bigfloats`.
