[Numpy-discussion] np 1.7b2 PyArray_BYTES(obj)=ptr fail

[Charles R Harris]

On Tue, Oct 2, 2012 at 11:30 AM, Frédéric Bastien <nouiz at nouiz.org> wrote:

> On Tue, Oct 2, 2012 at 1:18 PM, Charles R Harris
> <charlesr.harris at gmail.com> wrote:
> >
> >
> > On Tue, Oct 2, 2012 at 9:45 AM, Frédéric Bastien <nouiz at nouiz.org>
> wrote:
> >>
> >> We implement our own subtensor(x[...], where ... can be index or
> >> slice) c code due to the way Theano work.
> >>
> >> I can probably change the logic, but if you plan to revert this
> >> interface changes, I prefer to wait for this change we someone else is
> >> doing other changes that would conflict. Also, I did a Theano release
> >> candidate and I really would like the final version to work with the
> >> next release of NumPy.
> >
> >
> > Well, you don't *have* to define NPY_NO_DEPRECATED_API. If you don't you
> can
> > access the array as before using the macros even for future versions of
> > numpy. The only way that could cause a problems is if the array
> structure is
> > rearranged and I don't think that will happen anytime soon. On that
> account
> > there has not been any discussion of reverting the changes. However, I'd
> > like f2py generated modules to use the new functions at some point and in
> > order to do that numpy needs to supply some extra functionality, I'm just
> > not sure of the best way to do it at the moment. If I had a good idea of
> > what you want to do it would help in deciding what numpy should provide.
>
> I do not define NPY_NO_DEPRECATED_API, so I get g++ warning about
> that. That is the problem I have.
>
> What I do is close to that:
>
> alloc a new ndarray that point to the start of the ndarray I want to
> view with the right number of output dimensions.
>
> Compute the new dimensions/strides and data ptr. Then set the data ptr
> to what I computed. Then set the base ptr.
>
> I can reverse this and create the ndarray only at the end, but as this
> change break existing code here, it can break more code. That is why I
> wrote to the list.
>
> doing "PyArray_BASE(xview) = ptr" work when I don't define
> NPY_NO_DEPRECATED_API, but do not work when I define
> NPY_NO_DEPRECATED_API. I would have expected the same for
> PyArray_BYTES/DATA.
>
> Do this explain clearly the problem I saw?
>
>
Yes, thanks. I see in ndarraytypes.h

#define PyArray_DATA(obj) ((void *)(((PyArrayObject_fields *)(obj))->data))

I wonder if the cast to void* is causing a problem? Could you try char*
instead?

Chuck
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