[Numpy-discussion] Proposed Roadmap Overview

Mark Wiebe mwwiebe@gmail....
Fri Feb 17 12:21:11 CST 2012


On Fri, Feb 17, 2012 at 11:52 AM, Eric Firing <efiring@hawaii.edu> wrote:

> On 02/17/2012 05:39 AM, Charles R Harris wrote:
> >
> >
> > On Fri, Feb 17, 2012 at 8:01 AM, David Cournapeau <cournape@gmail.com
> > <mailto:cournape@gmail.com>> wrote:
> >
> >     Hi Travis,
> >
> >     On Thu, Feb 16, 2012 at 10:39 PM, Travis Oliphant
> >     <travis@continuum.io <mailto:travis@continuum.io>> wrote:
> >      > Mark Wiebe and I have been discussing off and on (as well as
> >     talking with Charles) a good way forward to balance two competing
> >     desires:
> >      >
> >      >        * addition of new features that are needed in NumPy
> >      >        * improving the code-base generally and moving towards a
> >     more maintainable NumPy
> >      >
> >      > I know there are load voices for just focusing on the second of
> >     these and avoiding the first until we have finished that.  I
> >     recognize the need to improve the code base, but I will also be
> >     pushing for improvements to the feature-set and user experience in
> >     the process.
> >      >
> >      > As a result, I am proposing a rough outline for releases over the
> >     next year:
> >      >
> >      >        * NumPy 1.7 to come out as soon as the serious bugs can be
> >     eliminated.  Bryan, Francesc, Mark, and I are able to help triage
> >     some of those.
> >      >
> >      >        * NumPy 1.8 to come out in July which will have as many
> >     ABI-compatible feature enhancements as we can add while improving
> >     test coverage and code cleanup.   I will post to this list more
> >     details of what we plan to address with it later.    Included for
> >     possible inclusion are:
> >      >        * resolving the NA/missing-data issues
> >      >        * finishing group-by
> >      >        * incorporating the start of label arrays
> >      >        * incorporating a meta-object
> >      >        * a few new dtypes (variable-length string,
> >     varialbe-length unicode and an enum type)
> >      >        * adding ufunc support for flexible dtypes and possibly
> >     structured arrays
> >      >        * allowing generalized ufuncs to work on more kinds of
> >     arrays besides just contiguous
> >      >        * improving the ability for NumPy to receive JIT-generated
> >     function pointers for ufuncs and other calculation opportunities
> >      >        * adding "filters" to Input and Output
> >      >        * simple computed fields for dtypes
> >      >        * accepting a Data-Type specification as a class or JSON
> file
> >      >        * work towards improving the dtype-addition mechanism
> >      >        * re-factoring of code so that it can compile with a C++
> >     compiler and be minimally dependent on Python data-structures.
> >
> >     This is a pretty exciting list of features. What is the rationale for
> >     code being compiled as C++ ? IMO, it will be difficult to do so
> >     without preventing useful C constructs, and without removing some of
> >     the existing features (like our use of C99 complex). The subset that
> >     is both C and C++ compatible is quite constraining.
> >
> >
> > I'm in favor of this myself, C++ would allow a lot code cleanup and make
> > it easier to provide an extensible base, I think it would be a natural
> > fit with numpy. Of course, some C++ projects become tangled messes of
> > inheritance, but I'd be very interested in seeing what a good C++
> > designer like Mark, intimately familiar with the numpy code base, could
> > do. This opportunity might not come by again anytime soon and I think we
> > should grab onto it. The initial step would be a release whose code that
> > would compile in both C/C++, which mostly comes down to removing C++
> > keywords like 'new'.
> >
> > I did suggest running it by you for build issues, so please raise any
> > you can think of. Note that MatPlotLib is in C++, so I don't think the
> > problems are insurmountable. And choosing a set of compilers to support
> > is something that will need to be done.
>
> It's true that matplotlib relies heavily on C++, both via the Agg
> library and in its own extension code.  Personally, I don't like this; I
> think it raises the barrier to contributing.  C++ is an order of
> magnitude more complicated than C--harder to read, and much harder to
> write, unless one is a true expert. In mpl it brings reliance on the CXX
> library, which Mike D. has had to help maintain.  And if it does
> increase compiler specificity, that's bad.
>

This gets to the recruitment issue, which is one of the most important
problems I see numpy facing. I personally have contributed a lot of code to
NumPy *in spite of* the fact it's in C. NumPy being in C instead of C++ was
the biggest negative point when I considered whether it was worth
contributing to the project. I suspect there are many programmers out there
who are skilled in low-level, high-performance C++, who would be willing to
contribute, but don't want to code in C.

I believe NumPy should be trying to find people who want to make high
performance, close to the metal, libraries. This is a very different type
of programmer than one who wants to program in Python, but is willing to
dabble in a lower level language to make something run faster. High
performance library development is one of the things the C++ developer
community does very well, and that community is where we have a good chance
of finding the programmers NumPy needs.

I would much rather see development in the direction of sticking with C
> where direct low-level control and speed are needed, and using cython to
> gain higher level language benefits where appropriate.  Of course, that
> brings in the danger of reliance on another complex tool, cython.  If
> that danger is considered excessive, then just stick with C.
>

There are many small benefits C++ can offer, even if numpy chooses only to
use a tiny subset of the C++ language. For example, RAII can be used to
reliably eliminate PyObject reference leaks.

Consider a regression like this:
http://mail.scipy.org/pipermail/numpy-discussion/2011-July/057831.html

Fixing this in C would require switching all the relevant usages of
NPY_MAXARGS to use a dynamic memory allocation. This brings with it the
potential of easily introducing a memory leak, and is a lot of work to do.
In C++, this functionality could be placed inside a class, where the
deterministic construction/destruction semantics eliminate the risk of
memory leaks and make the code easier to read at the same time. There are
other examples like this where the C language has forced a suboptimal
design choice because of how hard it would be to do it better.

Cheers,
Mark


> Eric
>
> >
> > Chuck
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