How do i work with pre-compiled libraries in cython?

Question

I'm trying to compile a quick extension for a module that was pre-compiled on install (.pyd). Below is a simplistic example of what i'm trying to do. Given foo.pyd:

baz.pxd

from foo.bar cimport Bar

cdef class Baz(Bar):
    pass

baz.pyx

cdef class Baz(Bar):
    def __init__(self, *a, **k):
        ...

setup.py

from distutils.core import setup
from Cython.Build import cythonize
from distutils.extension import Extension

extensions = [Extension('baz', ['baz.pyx',], libraries=['foo.pyd',])]
setup(name='baz', ext_modules=cythonize(extensions))

I've tried many variations of the above, to no avail.

Answer 1

cimport is for C/C++ APIs (functions, structs, classes) and reads from .pxd files, which are the Cython counterpart to C/C++ headers. If you don't have a .pxd for the foo library at compile-time, you cannot cimport from it. Python extension modules (.pyd on Windows, .so on Linux) typically don't have C APIs at all: they only contain externally visible symbols that allow the Python module importer to recognize their contents as a Python module.

Also, if you want to get a Python class (even one implemented as an extension type) from a module, you need to import it. I don't think a cdef class is allowed to inherit from such a class, though.