[Numpy-discussion] Zeros in strides

[Sasha]

On 2/2/06, Travis Oliphant <oliphant.travis at ieee.org> wrote:
> The changes you describe, however, require serious thought with C-level
> explanations because you will be changing some fundamental assumptions
> that are made throughout the code.
>

I agree, but I would like to discuss this at the conceptual level
first and maybe hear from  people not intimately familiar with the C
code about what they would expect from a zero stride.

> For example, currently there is no way you can construct new memory for
> an array and have different strides assigned (that's why strides is
> ignored if no buffer is given).  You would have to  change the behavior
> of the C-level function PyArray_NewFromDescr.   You need to propose how
> exactly you would change that.
>
Sure.  I've started working on a "proof of concept" patch and will post it soon.


> Checking for strides that won't cause later segfaults can be tricky
> especially if you start allowing buffer-sizes to be different than array
> dimensions.   How do you propose to ensure that you won't walk outside
> of allocated memory when somebody changes the strides later?
>
I think PyArray_CheckStrides would catch that, but I will have to test
that once I have some code ready.


> I'm concerned that your proposal has too many potential pitfalls.  At
> least you haven't addressed them sufficiently.   My current inclination
> is to simply disallow setting the strides attribute now that the
> misaligned segments of code have been tested.

That would be an unfortunate result of my post :-(  I would suggest
just to disallow zero strides in PyArray_CheckStrides until I can
convince you that they are not that dangerous.