[PYTHON MATRIX-SIG] NumPy and PIL extension module

[Jean-Bernard ADDOR]

If I understand right, array are not accessed throught iterators ?


A bientot,

	Jean-Bernard


On Mon, 5 May 1997, Konrad Hinsen wrote:

> > Most of what I need the data for will probably require floating point
> > values -- this isn't really the big issue for me though.  Could someone
> > post how to access and change an array element in an efficient manner in C
> > (ie. not a lot of Python overhead)?  The code in multiarraymodule isn't
> > well commented so I don't really understand what is going on.
> 
> If you have to access an arbitrary array, things become a bit
> complicated. It is much easier to deal with contiguous arrays.
> A newly created array is always contiguous, for example, as are
> arrays that are the result of any computation. Only indexing and
> other structural operations create non-contiguous arrays.
> 
> You can ensure that you are dealing with a contiguous array by calling
> PyArray_ContiguousFromObject(). This function will return a contiguous
> array unchanged, and return a contiguous copy for a non-contiguous
> array. Only if you can't affort the overhead of a potential copy
> you should try to deal with arbitrary arrays - in which case I
> can only wish you good luck ;-)
> 
> Now for accessing contiguous arrays. If "array" is a variable
> of type PyArrayObject, then array->data points to its data space.
> You will have to cast this to the correct pointer type according
> to the type of the elements. The data is organized just like in
> a statically allocated C array, i.e. the last index varies fastest.
> 
> So all you need is the information about the shape to be able to
> access anything you want. And that's easy: the number of dimensions is
> array->nd, and the list of dimensions is pointed to by
> array->dimensions.
> 
> I expect that eventually we'll want better C API support for
> accessing arrays, but I suppose it won't happen soon...
> -- 
> -------------------------------------------------------------------------------
> Konrad Hinsen                          | E-Mail: hinsen@ibs.ibs.fr
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