[PyKDE] Using numpy/numarray in custom C++ code and exposing with sip

[Claus, Richard]

Hi Ulrich & Gerard,

  Your discussion about numpy/numarray usage by pyQwt piqued my interest.  Could one of you please post a snippet of code showing how one exposes an array of, say, unsigneds, in custom C++ code as a numpy and/or numarray array in python via sip, or point me to where I can learn how to do this?  I tried to discover how to do this once but gave up due to time constraints.

  Thanks very much.

	Ric


> -----Original Message-----
> From: Gerard Vermeulen [mailto:gvermeul at grenoble.cnrs.fr] 
> Sent: Monday, February 02, 2004 12:00 AM
> To: ulrich.berning at t-online.de
> Cc: pykde at mats.imk.fraunhofer.de
> Subject: Re: [PyKDE] How to add handwritten *.cpp files to a 
> sip generated module with configure.py
> 
> 
> On Mon, 02 Feb 2004 00:15:35 +0100
> ulrich.berning at t-online.de (Ulrich Berning) wrote:
> 
> > Gerard Vermeulen schrieb:
> > 
> > >Hi Phil,
> > >
> > >Ulrich Berning kindly provided me with code to build PyQwt with 
> > >configure.py.
> > >
> > >One of his changes was to put a few handwritten *.cpp files to 
> > >interface the Numerical Python extension modules (numpy 
> and numarray) 
> > >in the qwtmod.sip file.
> > >
> > >The problem is that there are conflicts between the header 
> files of 
> > >numpy and numarray (numarray should become the successor 
> of numpy, so 
> > >there is an overlap in their API). Putting all the 
> interface code in 
> > >the qwtmod.sip file leads to compile errors because of the 
> inclusion 
> > >of the conflicting headers in the same .cpp file.
> > >
> > >Ulli did not see it, because he is only having numpy, I guess.
> > >
> > >  
> > >
> > Yes, this is true. I can't see why I should have numpy AND numarray.
> > Because numarry will be the successor of numpy someday, but 
> currently it 
> > is not, I choosed to stay with numpy. The only reason to 
> support numpy 
> > AND numeric could be to provide a binary module that works 
> either with 
> > numpy or with numarray or with none of them. But then, the 
> interface 
> > code needs some modifactions. You have to find out in the 
> init function 
> > if numpy or numarray or none of both is available. Simply calling 
> > import_array() and/or import_libnumarray() does not work. 
> If you call 
> > import_libnumarray() when nummarray is not installed you get a 
> > Py_FatalError().
> > 
> > And at least, if I take a look at Numeric/arrayobject.h and
> > numarray/arrayobject.h, I can see the following:
> > 
> > in Numeric/arrayobject.h:
> > #ifndef Py_ARRAYOBJECT_H
> > #define Py_ARRAYOBJECT_H
> > 
> > in numarray/arrayobject.h:
> > #ifdef Py_ARRAYOBJECT_H
> > #error "Can't use numarray Numeric compatability *and* 
> Numeric in same
> > module"
> > #endif
> > 
> > My recommendation is, either numpy is used, if it is there 
> OR numarray
> > if it is there OR none of them. Using the numpy API AND the 
> numarray API 
> > in the same module may work, but was not intended by the Numerical 
> > Python Group and seems to be dangerous.
> > 
> PyQwt is able to import both, since version 3.7 and since 
> version 3.8 it includes numarray/libnumarray.h. It really 
> works in the same Python program but it requires that calls 
> to the Numeric API and numarray API are split into different 
> source files (importing a C API from a C/C++ extension module 
> is nothing else than setting up a table with pointers to 
> functions into the module).
> 
> I provide the possibility to use both so that people can make 
> the transition. It also facilitates support and testing. 
> 
> The purpose of my mail was to point out a facility that is 
> lacking from Phil's new build system (but I can hack my way 
> out).  It explains also why I am sticking so long with my own 
> tools which are lacking in other respects.
> 
> Gerard
> 
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