[pypy-dev] offtopic, ontopic, ... (was: ctypes - PyPy 1.8 slower than Python 2.6.5)

[Stefan Behnel]

Maciej Fijalkowski, 13.02.2012 19:44:
> On Mon, Feb 13, 2012 at 4:29 PM, Stefan Behnel wrote:
>> Sébastien Volle, 13.02.2012 13:33:
>>> My team is working on a project of fast packet sniffers and I'm comparing
>>> performance between different languages.
>>> So, we came up with a simple ARP sniffer that I ported to Python using
>>> ctypes.
>>
>> If performance is important to you, you may want to write the wrapper for
>> Python in Cython instead (and maybe also parts of the filtering code, which
>> I assume your program to be about).
> 
> I appreciate your willingness to advertise cython wherever it's
> possible, but this is simply not on topic on the current thread.

Sébastien Volle replied to my mail telling me that their current approach
was actually based on LuaJIT and its native FFI, and that he was mostly
comparing that to other languages (which all loose thoroughly in the
competition, BTW). That makes Cython on-topic for him at least.

I also find Cython generally *very* on-topic when the intention is to
interface Python code with C code, especially when performance and/or ease
of use are part of the requirements. In terms of features and comfort,
ctypes is still a bit too far behind the user experience that Cython has to
offer. Given how important Cython has become for the Python ecosystem in
many regards, it's sad that PyPy still doesn't have it available. From what
I hear, that's a serious blocker to some users. (Or should I say "most users"?)


> Cython is not a panacea for all woes

Well, what is?


> and it's actually slower than
> pypy on most cases that don't involve calling C. It's also slower even
> when you provide direct type annotations

Ah, "most cases", hm? How is that for a well founded statement? What are
you using for comparison? speed.pypy.org? Have you noticed that amongst all
those benchmarks there that PyPy was specifically tuned for, there is not a
single benchmark that was selected specifically for Cython? There are
always lies, damn lies and then there are benchmarks, don't forget that.


> so you have a pretty
> reasonable usecase for pypy even in cases where calling C is a
> problem. Also, we're going to attack those ctypes problems.

Since when is "we can do that, too" synonymous with "there are no
alternatives"? World domination seems an attractive goal to go after, but
it's pretty boring in the long run.

Besides, "going to attack" admits that you're not there yet. Cython has
been there for a couple of years now, it solves real problems that real
users have today, and it's constantly getting better in doing so, because
it's being designed and developed to solve those problems.

It may not be obvious to you, but PyPy isn't a panacea either.


> If you wish to respond to my mail, please put it into a post that has
> a different title and not hijack all the discussions with cython.

Ok, done. BTW, what are those show-off mails meant for that you keep
sending to python-dev on each PyPy release? Do you really consider them
on-topic for the development of the CPython runtime, or even just the
Python language? Food for thought ...

Stefan