Numerical Python

Sebastian Haase wrote:

>Hi,
>What is the C API to make an array that got allocated,
>let's say, by  a = new short[512*512],
>accessible to python as numarray.
>
What you want to do is not currently supported well in C.  The way to do 
what you want is:

1.  Create a buffer object from your C++ array.  The buffer object can 
be built such that it refers to the original copy of the data.

2.  Call  back into Python (numarray.NumArray) with your buffer object 
as the buffer parameter.

You can scavenge the code in NA_newAll (Src/newarray.ch) for most of the 
callback.

>I tried NA_New - but that seems to make a copy.
>I would need it to use the original memory space
>so that I can "observe" the array from Python WHILE
>the underlying C array changes (it's actually a camera image)
>
That sounds cool!

>
>Thanks,
>Sebastian Haase
>
>
>
>
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Hi - I hope it's OK to just resent my posting from Feb 22.
I didn't get any response at the time.
Also - looking into the code again - I am wondering what the best way to
handle the reference counting would be ?
Here come my original posting:

> Short follow up:
> 1) Is it planned to support this more directly?
> 2) How much does it cost to create a buffer object if it
> uses my already allocated memory ?
> 3) Can I change the pointer so that it points to a
> different memory space WITHOUT having to recreate any
> python objects? Or would that "confuse" the buffer or
> numarray?    (We are hoping to aquire 30 images per second
> - the images should get written into a circular buffer so
> that the data can be written to disk in larger chunks -
> but the python array should always refer to the current
> image )
>
> Thanks for all the nice toys (tools) ;-)
> Sebastian Haase
>
>
>
> On Fri, 17 Jan 2003 18:16:01 -0500
>   Todd Miller <jmiller@...> wrote:
> >Sebastian Haase wrote:
> >
> >>Hi,
> >>What is the C API to make an array that got allocated,
> >>let's say, by  a = new short[512*512],
> >>accessible to python as numarray.
> >>
> >What you want to do is not currently supported well in C.
> > The way to do what you want is:
> >
> >1.  Create a buffer object from your C++ array.  The
> >buffer object can be built such that it refers to the
> >original copy of the data.
> >
> >2.  Call  back into Python (numarray.NumArray) with your
> >buffer object as the buffer parameter.
> >
> >You can scavenge the code in NA_newAll (Src/newarray.ch)
> >for most of the callback.
> >
> >>I tried NA_New - but that seems to make a copy.
> >>I would need it to use the original memory space
> >>so that I can "observe" the array from Python WHILE
> >>the underlying C array changes (it's actually a camera
> >>image)
> >>
> >That sounds cool!
> >
> >>
> >>Thanks,
> >>Sebastian Haase