Compile cython modules

It took me a while to figure out how to import cython modules. Here is a configuration that works:

├── hn2016_falwa
│   ├── cython_modules
│   |   ├── pyx_modules
|   |   |   ├── __init__.py
|   |   |   ├── dirinv_cython.pyx
|   |   ├──setup_cython.py
|   |   ├──check_import.py
...

In dirinv_cython.pyx I have:

def x_sq_minus_x(x):
    return x**2 - x

In setup_cython.py I have:

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

setup(name='dirinv_cython',
      package_dir={'pyx_modules': ''},
      ext_modules=cythonize("pyx_modules/dirinv_cython.pyx"))

First, I compile the cython modules by executing in the directory cython_modules:

python setup_cython.py build_ext --inplace

This produces dirinv_cython.c in the directory pyx_modules/.

Put this in __init__.py:

import dirinv_cython

Then I run the script to test the imports check_import.py:

from pyx_modules import dirinv_cython

ans = dirinv_cython.x_sq_minus_x(19)
print(f"ans = {ans}")

Executing check_import.py gives

ans = 342