That’s a creative use of a custom
2to3 fixer [1] to transform the calculations [2]. Too bad this will no longer work with the removal of
2to3 in Python 3.13.
[1]: https://docs.python.org/3/library/2to3.html#fixers
[2]: https://github.com/rescrv/napkin/blob/e6a4de2/napkin/substit...