Cython assumes any function not annotated with @cython.cfunc is just a Python function, and not convertible to pure C. You can fix this by editing the def f declaration to read: @cython.cfunc def ...

The developers behind Cython, the Python library for compiling Python code to C, have at last released Cython 3.0 after many years of development and refinement.. The main goal behind Cython is to ...