Re: [Swig-user] converting c float array to numpy array or python list

[Rich E <rea...@gm...>]

On Mon, Dec 1, 2008 at 8:43 PM, Christopher Barker
<Chr...@no...> wrote:
> Rich E wrote:
>>
>> So I have a nice C library wrapped in python and I'd like to start
>> doing some plots of things in python... the problem is the data is all
>> stuck in C arrays.
>
>> But how would I go about returning a python list of the entire array,
>> or even better, an NumPy array?
>
> there is a numpy.i file distributed with numpy ( or with the docs, anyway).
> There was also a recent post on the numpy list with some extra hints and
> examples for using it.
>
> This is another nice article about it:
>
> http://matt.eifelle.com/2008/11/04/exposing-an-array-interface-with-swig-for-a-cc-structure/

After looking at this example, I have to admit that I am a bit
befuddled.  I also couldn't get the code to work, but this is probably
because I am not understanding the example.  So, I'll ask a couple
questions here and if there is a better place to do this, please let
me know.

In the example, Matt is converting data in a c struct.. all I want to
do is, provided a pointer to a c array and the size of the array,
convert it to a numpy array.  Hopefully then I will not have to write
a wrapper for every type of struct I have (and even worse, every
function that handles pointers to arrays).

I would think such a function could be quite general, enough to even
be included with numpy.  Matt's code is quite specific to the struct
he is handling and it is difficult to see what is necessary for my
very minimal needs.

>
>> My thoughts are that I will have to convert between C arrays and
>> python types (list or NumPy) quite often, probably at a refresh rate
>> suitable for animation.
>
> the above allow a numpy array and your C-code to share the same pointer, so
> it is very fast.
>
> -Chris
>
>
> --
> Christopher Barker, Ph.D.
> Oceanographer
>
> Emergency Response Division
> NOAA/NOS/OR&R            (206) 526-6959   voice
> 7600 Sand Point Way NE   (206) 526-6329   fax
> Seattle, WA  98115       (206) 526-6317   main reception
>
> Chr...@no...
>