[Python-Dev] Use of Cython (original) (raw)

Yury Selivanov yselivanov.ml at gmail.com
Tue Sep 4 15:51:37 EDT 2018

On Tue, Sep 4, 2018 at 2:58 PM Stefan Behnel <stefan_ml at behnel.de> wrote: [..]

Cython has four ways to provide type declarations: cdef statements in Cython code, external .pxd files for Python or Cython files, special decorators and declaration functions, and PEP-484/526 type annotations.

Great to hear that PEP 484 type annotations are supported. Here's a link to the docs: https://cython.readthedocs.io/en/latest/src/tutorial/pure.html#static-typing

[..]

> I know that Cython has a mode to use decorators in > pure Python code to annotate types, but they are less intuitive than > using typing annotations in 3.6+.

You can use PEP-484/526 type annotations to declare Cython types in Python code that you intend to compile. It's entirely up to you, and it's an entirely subjective measure which "is better". Many people prefer Cython's non-Python syntax because it allows them to apply their existing C knowledge. For them, PEP-484 annotations may easily be non-intuitive in comparison.

Yeah, but if we decide to use Cython in CPython we probably need to come up with something like PEP 7 to recommend one particular style and have an overall guideline. Using PEP 484 annotations means that we have pure Python code that PyPy and other interpreters can still run.

[..]

> I'd be +0.5 on using Cython (optionally?) to compile some pure Python > code to make it 30-50% faster. asyncio, for instance, would certainly > benefit from that.

Since most of this (stdlib) Python code doesn't need to stay syntax compatible with Python < 3.6 (actually 3.8) anymore, you can probably get much higher speedups than that by statically typing some variables and functions here and there. I recently tried that with difflib, makes a big difference.

I'd be willing to try this in asyncio if we start using Cython.

Yury

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