[Numpy-discussion] Best way to expose std::vector to be used with numpy

[Nathaniel Smith]

If the goal is to have something that works kind of like the new buffer
protocol but with a wider variety of python versions, then you might find
the old array interface useful:
http://docs.scipy.org/doc/numpy/reference/arrays.interface.html

I always get confused by the history here but I believe that that's the
numpy-only interface that later got cleaned up and generalized to become
the new buffer interface. Numpy itself still supports it.

-n
On 14 Oct 2014 11:19, "Daniele Nicolodi" <daniele at grinta.net> wrote:

> On 14/10/14 04:39, Charles R Harris wrote:
> > On Mon, Oct 13, 2014 at 12:54 PM, Sebastian Berg
> > <sebastian at sipsolutions.net <mailto:sebastian at sipsolutions.net>> wrote:
> >
> >     On Mo, 2014-10-13 at 13:35 +0200, Daniele Nicolodi wrote:
> >     > Hello,
> >     >
> >     > I have a C++ application that collects float, int or complex data
> in a
> >     > possibly quite large std::vector. The application has some SWIG
> >     > generated python wrappers that expose this vector to python.
> However,
> >     > the standard way in which SWIG exposes the data is to create a
> touple
> >     > and pass this to python, where it is very often converted to a
> numpy
> >     > array for processing. Of course this is not efficient.
> >     >
> >     > I would like therefore to generate a smarter python interface. In
> python
> >     > 3 I would without doubt go for implementing the buffer protocol,
> which
> >     > enables seamless interfacing with numpy. However, I need to
> support also
> >     > python 2 and there the buffer protocol is not as nice.
> >
> >     Isn't the new buffer protocol in python 2.6 or 2.7 already? There is
> at
> >     least a memoryview object in python 2, which maybe could be used to
> the
> >     same effect?
> >
> > No memoryview in python2.6, but the older buffer protocol it there. Is
> > Boost Python an option?
>
> The old buffer protocol is an option, but it is much less nice than the
> new one, as it requires to use numpy.frombuffer() with an exlicit dtype
> instead of the siumpler numpy.asarray() sufficient in python 3.
>
> Boost Python may be an option as the codebase already depends on Boost,
> but probably not yet on Boost Python. Can you point me to the relevant
> documentation, and maybe to an example? One of the problems I have is
> that the current wrapping is done auto-magically with SWIG and I would
> like to deviate the less possible from that patter.
>
> Thank you!
>
> Cheers,
> Daniele
>
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