[ase-users] Opinion about potentially adding Cython as a dependency

[Gaël Donval]

Dear list,

I am currently working on some geometrical code that I will ultimately
propose adding to ASE. I am currently using Cython to speed up what
needs speeding up and, to a more limited extent, I also use it to very
conveniently generate bindings to C.

The question is: would anyone see using Cython as a problem?

I know that the fewer dependencies, the better. However Cython is
almost as ubiquitous as Scipy nowadays in Python's scientific stack.

The only real drawbacks I can think of (and I can read about on the
internet) are pain points on Windows and incompatibility with different
Python implementations (e.g. PyPy). However, with pip wheels, Windows
is a non problem (most Python distributions on Windows now also include
Cython by default so manual compilation is far from the pain it used to
be) and ASE/GPAW do not support PyPy anyway because of all the C
dependencies.

Note that I am *not* proposing to convert any existing code to Cython
nor to use Cython by default. I am talking about specific cases which
would currently be handled by writing pure C code.

Best regards,
Gaël