[Numpy-discussion] swig numpy2carray converters

Matthieu Brucher matthieu.brucher@gmail....
Tue Nov 20 08:31:43 CST 2007


2007/11/20, Georg Holzmann <grh@mur.at>:
>
> Hallo!
>
> > Really?  I worked pretty hard to avoid copies when they were not
> > necessary.  For the ARGOUT typemaps, I allocate an array of the
> > requested size and then pass its data buffer to your function.  If
>
> Yes but this means that you again allocate an array of the same size.



Well, this is logical as you want a new argument in output.


E.g. in my algorithm I can have a very big internal matrix in C++ (say
> 700 MB - in fortran style). Now I want to have this matrix in numpy to
> plot some parts of it, get some data out of it ... whatever - if I again
> allocate an array of the same size, I am out of memory.
> Therefore I simply used the PyArray_FromDimsAndData() function to
> allocate the array.



This is why you use INPLACE typemaps that will NOT copy your data.


> that is not what you want, then you should probably be using the
> > INPLACE typemap.
>
> Yeah, but this results in the same as above ...



Are you sure ? Because the original object is not modified, so it is still
the same data.

If what you want is to provide a view  from your C++ matrix, this is
different. You must either :
- propose the array interface
- use a Python object inside your C++ matrix (this is to be done, I've a
basic example in my blog)

Matthieu
-- 
French PhD student
Website : http://miles.developpez.com/
Blogs : http://matt.eifelle.com and http://blog.developpez.com/?blog=92
LinkedIn : http://www.linkedin.com/in/matthieubrucher
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