setup.py

# DO NOT reorder these imports due to monkey-patch
from pybind11.setup_helpers import Pybind11Extension
from distutils.core import setup, Extension
import subprocess

cpython_mod = Extension('sum_from_cpython', sources=['src/sum_cpython.c'])
pybind_mod = Pybind11Extension('sum_from_pybind11',
                               sources=['src/sum_pybind11.cpp'])

subprocess.run(["swig", "-outcurrentdir", "-python", "src/swig_sum.i"])
swig_mod = Pybind11Extension('_swig_example',
                             sources=['swig_sum_wrap.c', 'src/sum.c'])

pybind_demo_mod = Pybind11Extension('pybind11_demo',
                                    sources=['src/pybind11_demo.cpp'])
setup(name='demo',
      version='0.0',
      description='This is a demo package',
      ext_modules=[cpython_mod, pybind_mod, swig_mod, pybind_demo_mod],
      py_modules=['swig_example'])