Porting a Simple Python module to Cython

Question

Let's say I have a directory "pylib" with this in it:

pylab/funcs.py:

def add(a, b):
    return a + b

pylab/__init__.py:

from .funcs import add

It is then possible to do the following:

$ python -c "import pylib as lib; print(lib.add(5, 6))"
11

How can I achieve the same effect with Cython with a similar organizational structure? That is, if I just have a single file, like:

cylab.pyx:

def add(a, b):
    return a + b

I can create a setup script

setup.py:

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

extensions = [ # I will eventually be referencing C libraries
    Extension('cylib', ['cylib.pyx'], libraries=[], library_dirs=[])
]

setup(
    ext_modules = cythonize(extensions)
)

and then the rest works in a fairly straightforward way

$ ./setup.py build_ext --inplace
[omitted]
$ python -c "import cylib as lib; print(lib.add(5, 6))"
11

but it is not clear to me how I'm supposed to break it up into separate files, nor how I'm supposed to modify the setup script once I do.

score 1 · Answer 1 · edited May 23 '17 at 10:31

It's not really possible to build a single Cython extension containing submodules. I think your best option is to build lots of individual Cython libraries.

Just rename all your .py to .pyx to generate a bunch of Cython extensions. The structure will be the same as it was before. I'd exclude the module __init__.py and keep that as pure Python (the rules for how Python finds modules in this case are a little more complicated.

You want to list all of your .pyx files as separate extensions in setup.py:

extensions = [ # I will eventually be referencing C libraries
    Extension('cylib.funcs', ['cylib/funcs.pyx'], libraries=[], library_dirs=[]),
    Extension('cylib.something_else', ['cylib/something_else.pyx'], libraries=[], library_dirs=[])
]

(and probably also tell setup.py that the whole cylib directory is a package, as you would when using distutils/setuptools with similar pure Python modules.)

Porting a Simple Python module to Cython

1 Answers1