Tool for automatically converting a pybind11 based project to nanobind

[blozano-tt]

Would it be feasible for the open source community to develop a tool that can automatically convert a code base that uses pybind11 to nanobind?

Motivation:

We have spent many months (> 6 months) trying to migrate a large code base from pybind11 to nanobind. Even after getting it to compile, we are seeing runtime issues. My colleague is attempting to write a custom clang-tidy check with FIXITs to do some conversion, because the python interface continues to change on main, and rebasing manually is a nightmare.

[oremanj]

Keep an eye on
#1140
pybind/pybind11#5800
which will hopefully make this process easier to do incrementally!

[wjakob]

Just FWIW: In my experience, LLM tools like Claude Code are super good at this kind of mechanical translation especially when combined with an existing test harness. (It's the kind of tedious/repetitive job that thing nobody enjoys doing by hand in any case.)

You can ask it to do a pass over the whole codebase and create a list of tricky corners first and propose a strategy, and then just launch a subagent per file that does the conversion. Then have it investigate test failures and fix the bindings while keeping the tests static.