I have implemented some very simple setuptools integration that circumvents the requirement to `import cython` in `setup.py` entirely, doing away with the century-old problem of having to importing requirements during installation:
<https://github.com/cython/cython/pull/477> This implementation is inspired by CFFI's setuptools integration: <https://cffi.readthedocs.org/en/latest/cdef.html#distutils-setuptools>. They do not require you to `import cffi` but simply define an additional keyword argument `cffi_modules` for `setup()`. This additional keyword argument _does not raise errors when cffi is not installed yet_ but can be used once cffi is there (as defined in `setup_requires`). Later setuptools will call cffi and have it do whatever it wants with the contents of the argument. Cython can do the exact same. Below you have the usual `setup.py`, with the chicken and egg `import` problem and a few `Extensions` that need to be `cythonize`d: import setuptools from Cython.Build import cythonize # this will fail if cython is not present prior to running `pip install this` from setuptools.extension import Extension extensions = [ Extension("fib", ["fib.pyx"]), Extension("fib2", ["fib2.pyx"]), ] setuptools.setup( name='example', version="1.0.0", packages=setuptools.find_packages(), setup_requires=['cython'], install_requires=['cython'], ext_modules=cythonize(extensions), ) With the changes I am proposing the usual ext_modules=cythonize(extensions), can be replaced with cython_modules=extensions, removing the need for `from Cython.Build import cythonize` and solving the import problem: import setuptools from setuptools.extension import Extension extensions = [ Extension("fib", ["fib.pyx"]), Extension("fib2", ["fib2.pyx"]), ] setuptools.setup( name='example', version="1.0.0", setup_requires=['cython'], # we must later require a Cython version that has this kind of integration install_requires=['cython'], cython_modules=extensions, ) This allows a nicer automated installation of tools that depend on cython and also allows end users to keep their `setup.py` cleaner and leaner. Additionally, I have also extended `cythonize()` a bit and thus allow for definitions like: import setuptools from setuptools.extension import Extension extensions = [ Extension("fib", ["fib.c"]), Extension("fib2", ["fib2.c"]), ] setuptools.setup( name='example', version="1.0.0", extras_require={'cython': ['cython']}, ext_modules=extensions, cython_modules=extensions, ) This will automatically compile pyx->c if cython is installed and a re-compilation is needed. Otherwise it will merely compile c->so. This allows devs to ship the generated C-code (as you suggest per your docs) but takes the heuristic to find out whether to compile pyx->C->so or only C->so completely out of `setup.py` and under control of cython. The change is written to be backwards compatible: - Using `cython_modules` is entirely optional and not using it is sideeffect-free - Having `cythonize()` internally automatically compile *.pyx files when *.c files are provided is disabled by default and must be enabled using the `replace_extension` keyword argument (`cython_modules` enables that option).
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