Re: void * C array to a Numpy array using Swig

Krish wrote: 
Hello People

I hope I am On Topic. Anyways, here is my problem. Any insights would
be really appreciated.

Posting to the numpy-discussion@xxxxxxxxxxxxxxxxxxxxx list would help generate more responses, I think.


I have wrapped a C IO module using SWIG -> Python Module. Suppose the
name of the module is "imageio" and the reader function from the file
is image_read() which returns an object ( "filled" C structure) with a
lot of members.

Let

a = imageio.image_read("testfile.image")

Now a is the object which contains pointer to data of the image. ( void
* pdata). ( a also contains the datatype which I need to typecast to
get the data pointed by pdata). My question is how to access the data
pointed by pdata in *Python*.

Yes, you are right that you need to use typemaps. It's been awhile since I did this kind of thing, but here are some pointers.

1)  Look at Michael Sanner's typemaps at

http://www.scripps.edu/mb/olson/people/sanner/html/Python/NumericTypemaps/

Except for the CHAR version, these should work for NumPy by replacing Numeric/arrayobject.h with numpy/arrayobject.h

2) In full scipy there are typemaps for numpy arrays in cluster/src/swig_num.i

Look here...

http://projects.scipy.org/scipy/scipy/file/trunk/Lib/cluster/src/swig_num.i

This should help you get started with some examples. Typemaps can be a little confusing at first, but they do make your interface a bit nicer.

-Travis

.

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