pymetabind is a single C header file that defines structures and simple inline functions which are intended to allow different Python binding frameworks (nanobind, pybind11, Boost.Python, SWIG, pyo3, ...), as well as different ABI versions of the same framework, to interoperate with each other. That is, functions bound using framework A can accept and return objects whose types are bound using framework B. (Different ABI versions of the same framework are treated like different frameworks would be.) Each participating framework can use this header to:
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publish lightweight information about its bound types, along with function pointers that allow other frameworks to interact with them, to a shared data structure located via a Python capsule object; and
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discover and use bindings published in this way by other frameworks.
Individual frameworks must implement support for pymetabind in order to be used with it. It is possible to implement only support for publishing bindings, or only support for using other frameworks' bindings, though of course the greatest interoperability benefits come from implementing both.
Currently, we are soliciting input from framework maintainers in order to confirm that the proposed interface will be widely implementable. You are encouraged to not publish any official release with pymetabind support during this time, since the ABI may still change. Experimentation, and PRs that make pymetabind a better fit for your framework, are welcome and encouraged!
All documentation is contained in the header file, pymetabind.h.
Copy pymetabind.h into the implementation of your binding framework and use the structures and inline functions found therein. To avoid coordination problems around installation, every framework is expected to keep its own copy. After a 1.0 release, we intend for changes to be very minimal and backward-compatible, so it is anticipated that keeping a copy up-to-date will not be burdensome.
pymetabind is licensed under the MIT license, which is included in a comment at the top of the single header file.
pymetabind was written by Joshua Oreman as part of his work with Hudson River Trading.