Distributing a shared library and some C code with a Cython extension module

Question

I\'m trying to take some functions from a large C++ shared library (libbig.so) and expose them to Python via Cython. To do so, I\'ve got a little C++ file (small.cpp) that provi

Answer 1

Here's my tricky solution. The idea is to "hide" the presence of cython until it's installed by the requirements. This can be achieved by lazy evaluation. Here's an example:

from setuptools import setup, Extension

class lazy_cythonize(list):
    def __init__(self, callback):
        self._list, self.callback = None, callback
    def c_list(self):
        if self._list is None: self._list = self.callback()
        return self._list
    def __iter__(self):
        for e in self.c_list(): yield e
    def __getitem__(self, ii): return self.c_list()[ii]
    def __len__(self): return len(self.c_list())

def extensions():
    from Cython.Build import cythonize
    ext = Extension('native_ext_name', ['your/src/*.pyx'])
    return cythonize([ext])


configuration = {
    'name': 'mypackage',
    'packages': ['yourpurepythonpackage'],
    'install_requires': ['cython==0.17'],
    'ext_modules': lazy_cythonize(extensions)
}

setup(**configuration)

lazy_cythonize is a fake list that generates its internal elements only when someone tries to access to it.
When it's required, this class imports Cython.Build and generates the list of extensions. This avoids to keep the *.c files in your project, requiring cython to be installed when the module is building.

Quite tricky, but actually it's working.