On 06/21/2012 02:59 PM, Stefan Behnel wrote:
Dag Sverre Seljebotn, 21.06.2012 14:05:
On 06/21/2012 01:36 PM, Stefan Behnel wrote:
On 06/21/2012 10:59 AM, Stefan Behnel wrote:
I find this worth fixing for 0.17:
http://trac.cython.org/cython_trac/ticket/780
I ran into this when I gave a Cython+NumPy course and this was the first
thing that the attendants tried when I asked them to validate that two
input arrays have the same size before adding them. It's the one obvious
way to do it, and it fails miserably. I think it should be fixed, and I
think it should be fixed soon because it feels really low-level and
complicated, especially to new users.
Can you clarify a bit -- did you give this course using np.ndarray[double,
ndim=2], or double[:, :]? They're really very separate under the hood and
the fix is different.
Or, did you actually use object[double, ndim=2] like in the bug report?
(Did me and Mark get around to propose deprecating this one on the list?)
IIRC, we used object[double, ndim=2] for both and I also tried it with a
memory view as in the bug report. I thought that using "object" was the
preferred way to do it? At least, it doesn't restrict the type of the
buffer exporter, which I consider a good thing.
That's a very theoretical argument as NumPy arrays are in practice the
only exporter.
I always teach np.ndarray[double...]. I've never told anyone about
object[...], I don't think it's in much use. For starters it's going to
be horribly inefficient unless you also add "mode='strided'" within the
brackets.
My proposal (and Mark's I think) is:
Since the memoryviews will neatly cover the general exporter case, and
since the [] syntax is much overloaded already (used for C++ templates
too), we should deprecate object[...] no matter what else happens.
Depending on what's decided for np.ndarray[...], we have:
Case A): Deprecate both np.ndarray[...] and object[...]
Case B): Only deprecate object[...], keep np.ndarray[...] (e.g., through
a decorator used in numpy.pxd on the ndarray type). So rather than
having a trailing [] mean buffers unless it means something else (like
C++ templates), we instead make np.ndarray a "template", through special
compiler support.
Dag
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