Interfacing Fortran with python in 2025

[ivanpribec]

@fracton

PS: I really like pybind11, and using it with cmake and setuptools to build a python package. I am looking for similar reliable solution to build my project in Fortran.

You could stick with pybind11 and just use gfortran to write the C headers for your bind(c) procedures (the ones implemented in Fortran):

Compilers supporting generation of C function prototypes

Among Fortran compilers, gfortran can be instructed to emit C function prototypes which can be put in a header file. Here’s how to do it with gfortran (see section Options for interoperability with other languages): $ gfortran -fc-prototypes -fsyntax-only foo.f90 > foo.h As an example, running the command above on the file ! foo.f90 module foo use, intrinsic :: iso_c_binding, only: c_float implicit none contains real(c_float) function foo_sqr(x) bind(c) real(c_float), intent(in) :: …

To generate the header use:

$ gfortran -fc-prototypes -fsyntax-only fortranlib.f90 > fortranlib.h

Then you can just follow your standard C/C++ + pybind11 workflow.

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I haven’t used pybind11 (or nanobind) before. Does a C function prototype contain all the needed information to write the pybind11 binding? If yes, there may be some ways to automate this. I’ve given a talk about something similar recently: FOSDEM 2025 - Easier API Interoperability: writing a bindings Generator to C/C++ with Coccinelle