[Numpy-discussion] Proposed Roadmap Overview

Matthew Brett matthew.brett@gmail....
Sat Feb 18 15:02:30 CST 2012


Hi,

On Sat, Feb 18, 2012 at 12:45 PM, Charles R Harris
<charlesr.harris@gmail.com> wrote:
>
>
> On Sat, Feb 18, 2012 at 1:39 PM, Matthew Brett <matthew.brett@gmail.com>
> wrote:
>>
>> Hi,
>>
>> On Sat, Feb 18, 2012 at 12:35 PM, Charles R Harris
>> <charlesr.harris@gmail.com> wrote:
>> >
>> >
>> > On Sat, Feb 18, 2012 at 12:21 PM, Matthew Brett
>> > <matthew.brett@gmail.com>
>> > wrote:
>> >>
>> >> Hi.
>> >>
>> >> On Sat, Feb 18, 2012 at 12:18 AM, Christopher Jordan-Squire
>> >> <cjordan1@uw.edu> wrote:
>> >> > On Fri, Feb 17, 2012 at 11:31 PM, Matthew Brett
>> >> > <matthew.brett@gmail.com> wrote:
>> >> >> Hi,
>> >> >>
>> >> >> On Fri, Feb 17, 2012 at 10:18 PM, Christopher Jordan-Squire
>> >> >> <cjordan1@uw.edu> wrote:
>> >> >>> On Fri, Feb 17, 2012 at 8:30 PM, Sturla Molden <sturla@molden.no>
>> >> >>> wrote:
>> >> >>>>
>> >> >>>>
>> >> >>>> Den 18. feb. 2012 kl. 05:01 skrev Jason Grout
>> >> >>>> <jason-sage@creativetrax.com>:
>> >> >>>>
>> >> >>>>> On 2/17/12 9:54 PM, Sturla Molden wrote:
>> >> >>>>>> We would have to write a C++ programming tutorial that is based
>> >> >>>>>> on
>> >> >>>>>> Pyton knowledge instead of C knowledge.
>> >> >>>>>
>> >> >>>>> I personally would love such a thing.  It's been a while since I
>> >> >>>>> did
>> >> >>>>> anything nontrivial on my own in C++.
>> >> >>>>>
>> >> >>>>
>> >> >>>> One example: How do we code multiple return values?
>> >> >>>>
>> >> >>>> In Python:
>> >> >>>> - Return a tuple.
>> >> >>>>
>> >> >>>> In C:
>> >> >>>> - Use pointers (evilness)
>> >> >>>>
>> >> >>>> In C++:
>> >> >>>> - Return a std::tuple, as you would in Python.
>> >> >>>> - Use references, as you would in Fortran or Pascal.
>> >> >>>> - Use pointers, as you would in C.
>> >> >>>>
>> >> >>>> C++ textbooks always pick the last...
>> >> >>>>
>> >> >>>> I would show the first and the second method, and perhaps
>> >> >>>> intentionally forget the last.
>> >> >>>>
>> >> >>>> Sturla
>> >> >>>>
>> >> >>
>> >> >>> On the flip side, cython looked pretty...but I didn't get the
>> >> >>> performance gains I wanted, and had to spend a lot of time figuring
>> >> >>> out if it was cython, needing to add types, buggy support for
>> >> >>> numpy,
>> >> >>> or actually the algorithm.
>> >> >>
>> >> >> At the time, was the numpy support buggy?  I personally haven't had
>> >> >> many problems with Cython and numpy.
>> >> >>
>> >> >
>> >> > It's not that the support WAS buggy, it's that it wasn't clear to me
>> >> > what was going on and where my performance bottleneck was. Even after
>> >> > microbenchmarking with ipython, using timeit and prun, and using the
>> >> > cython code visualization tool. Ultimately I don't think it was
>> >> > cython, so perhaps my comment was a bit unfair. But it was
>> >> > unfortunately difficult to verify that. Of course, as you say,
>> >> > diagnosing and solving such issues would become easier to resolve
>> >> > with
>> >> > more cython experience.
>> >> >
>> >> >>> The C files generated by cython were
>> >> >>> enormous and difficult to read. They really weren't meant for human
>> >> >>> consumption.
>> >> >>
>> >> >> Yes, it takes some practice to get used to what Cython will do, and
>> >> >> how to optimize the output.
>> >> >>
>> >> >>> As Sturla has said, regardless of the quality of the
>> >> >>> current product, it isn't stable.
>> >> >>
>> >> >> I've personally found it more or less rock solid.  Could you say
>> >> >> what
>> >> >> you mean by "it isn't stable"?
>> >> >>
>> >> >
>> >> > I just meant what Sturla said, nothing more:
>> >> >
>> >> > "Cython is still 0.16, it is still unfinished. We cannot base NumPy
>> >> > on
>> >> > an unfinished compiler."
>> >>
>> >> Y'all mean, it has a zero at the beginning of the version number and
>> >> it is still adding new features?  Yes, that is correct, but it seems
>> >> more reasonable to me to phrase that as 'active development' rather
>> >> than 'unstable', because they take considerable care to be backwards
>> >> compatible, have a large automated Cython test suite, and a major
>> >> stress-tester in the Sage test suite.
>> >>
>> >
>> > Matthew,
>> >
>> > No one in their right mind would build a large performance library using
>> > Cython, it just isn't the right tool. For what it was designed for -
>> > wrapping existing c code or writing small and simple things close to
>> > Python
>> > - it does very well, but it was never designed for making core C/C++
>> > libraries and in that role it just gets in the way.
>>
>> I believe the proposal is to refactor the lowest levels in pure C and
>> move the some or most of the library superstructure to Cython.
>
>
> Go for it.

My goal was to try and contribute to substantive discussion of the
benefits / costs of the various approaches.  It does require a
realistic assessment of what is being proposed.  It may be, that
discussion is not fruitful.  But then we all lose, I think,

Best,

Matthew


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