[C++-sig] Status of Numpy support in boost python

[Hans Meine]

Am Montag 08 März 2010 13:32:22 schrieb Pim Schellart:
> we are working on a project for which it would be extremely useful if
> numpy arrays could be passed as arguments to wrapped C++ methods.
> On the website I cannot find any evidence that this is currently
> supported by Boost Python.
> Is this (or will this be) implemented?

After all the recent discussion, I want to point to yet another (hopefully) 
interesting bit of code which I am involved with:

Our "vigra" (computer vision) library now comes with numpy- and BPL-based 
python bindings.

In addition to type-safe conversions between C++ and Python(*), this offers a 
vigra::MultiArray on the C++ side, which is an n-dimensional array class 
template, complete with n-dimensional iterators (using raw pointers for the 
innermost dimension to offer the best possible performance for unstrided 
arrays) and a lot of algorithms, i.e. pointwise transformation / [possibly 
type-coercing] copying / inspection etc.

One particular feature Ulli is proud of is the automatic conversion to 
*subclasses* of ndarray, such that we can register and use e.g. 'Volume' 
python classes for 3D arrays.

I really want to stress that VIGRA is a very versatile template library which 
should be able to work in conjunction with any other libraries and data 
structures, i.e. true generic code (usually you don't even need to compile 
VIGRA, if you are not interested in an image import/export library).  So don't 
hesitate to give it a shot even if you are /not/ interested in any of its 
array / linalg algorithms.  (Actually, the PythonArray template class should 
be even useful without boost::python, i.e. I am using it with SIP, too.)

I don't think there will ever be just /one/ single solution for 
boost::python+numpy, since everyone seems to have different 
requirements/expectations w.r.t. available algorithms, static vs. dynamic 
element types etc.

However, I do think that our vigranumpy approach could be very useful for some 
of this list's readers.

HTH,
  Hans
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