old_contents: #!/usr/bin/env python3
  
  from distutils.core import setup
  from distutils.extension import Extension
  from Cython.Distutils import build_ext
  
  setup(
      cmdclass = {'build_ext': build_ext},
      ext_modules = [Extension("vapoursynth", ["src/cython/vapoursynth.pyx"])]
  )
  
new_contents: #!/usr/bin/env python3
  
  from os import pardir
  from os.path import join
  from distutils.core import setup
  from distutils.extension import Extension
  from Cython.Distutils import build_ext
  
  setup(
      cmdclass = {'build_ext': build_ext},
      ext_modules = [Extension('vapoursynth', ['src/cython/vapoursynth.pyx'],
                               include_dirs = ['.', join(pardir, 'src', 'cython')])]
  )
  
subject: Add include paths to setup.py.