[Galanwe]

I found PyO3 to be a bit weird to use. There's plenty of documentation, but it's kind of vague on the general basic concepts, which makes the library hard to understand (even though I have a background in writing CPython extensions in C).

Also, once you play with it more than 30m, you quickly realize that struct attributes are copied all over the place... which is not only slow, but more sadly any mutable function on an attribute will just silently modify a temporary copy...