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

Sebastian Berg sebastian at sipsolutions.net
Mon Oct 13 14:54:28 EDT 2014

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?

- Sebastian

> What is the best thing to do to expose the data buffer to python 2,
> without introducing a dependency on numpy in the application?
> Bonus points if the proposed solution comes with a pointer on how to
> implement in in SWIG (which I don't know much and feel a bit too magic
> for my taste).
> Thank you!
> Cheers,
> Daniele
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