[Python-Dev] Use of Cython

Yury Selivanov yselivanov.ml at gmail.com
Tue Aug 7 13:34:32 EDT 2018

On Mon, Aug 6, 2018 at 11:49 AM Ronald Oussoren via Python-Dev
<python-dev at python.org> wrote:

> I have no strong opinion on using Cython for tests or in the stdlib, other than that it is a fairly large dependency.  I do think that adding a “Cython-lite” tool the CPython distribution would be less ideal, creating and maintaining that tool would be a lot of work without clear benefits over just using Cython.

Speaking of which, Dropbox is working on a new compiler they call "mypyc".

mypyc will compile type-annotated Python code to an optimized C. The
first goal is to compile mypy with it to make it faster, so I hope
that the project will be completed. Essentially, mypyc will be similar
to Cython, but mypyc is a *subset of Python*, not a superset.
Interfacing with C libraries can be easily achieved with cffi. Being a
strict subset of Python means that mypyc code will execute just fine
in PyPy. They can even apply some optimizations to it eventually, as
it has a strict and static type system.

I'd be more willing to start using mypyc+cffi in CPython stdlib
*eventually*, than Cython now.  Cython is a relatively complex and
still poorly documented language.  I'm speaking from experience after
writing thousands of lines of Cython in uvloop & asyncpg.  In skillful
hands Cython is amazing, but I'd be cautious to advertise and use it
in CPython.

I'm also -1 on using Cython to test C API. While writing C tests is
annoying (I wrote a fair share myself), their very purpose is to make
third-party tools/extensions more stable. Using a third-party tool to
test C API to track regressions that break third-party tools feels


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