[Cython] buffer syntax vs. memory view syntax

Dag Sverre Seljebotn d.s.seljebotn at astro.uio.no
Mon May 7 18:00:20 CEST 2012

On 05/07/2012 04:16 PM, Stefan Behnel wrote:
> Stefan Behnel, 07.05.2012 15:04:
>> Dag Sverre Seljebotn, 07.05.2012 13:48:
>>> BTW, with the coming of memoryviews, me and Mark talked about just
>>> deprecating the "mytype[...]" meaning buffers, and rather treat it as
>>> np.ndarray, array.array etc. being some sort of "template types". That is,
>>> we disallow "object[int]" and require some special declarations in the
>>> relevant pxd files.
>> Hmm, yes, it's unfortunate that we have two different types of syntax now,
>> one that declares the item type before the brackets and one that declares
>> it afterwards.
> I actually think this merits some more discussion. Should we consider the
> buffer interface syntax deprecated and focus on the memory view syntax?

I think that's the very-long-term intention. Then again, it may be too 
early to really tell yet, we just need to see how the memory views play 
out in real life and whether they'll be able to replace 
np.ndarray[double] among real users. We don't want to shove things down 
users throats.

But the use of the trailing-[] syntax needs some cleaning up. Me and 
Mark agreed we'd put this proposal forward when we got around to it:

  - Deprecate the "object[double]" form, where [dtype] can be stuck on 
any extension type

  - But, do NOT (for the next year at least) deprecate 
np.ndarray[double], array.array[double], etc. Basically, there should be 
a magic flag in extension type declarations saying "I can be a buffer".

For one thing, that is sort of needed to open up things for templated 
cdef classes/fused types cdef classes, if that is ever implemented.

The semantic meaning of trailing [] is still sort of like the C++ 
meaning; that it templates the argument types (except it's lots of 
special cases in the compiler for various things rather than a 
Turing-complete template language...)


> The words-to-punctuation ratio of the latter may hurt the eyes when
> encountering it unprepared, but at least it doesn't require two type names,
> of which the one before the brackets (i.e. "object") is mostly useless.
> (Although it does reflect the notion that we are dealing with an object
> here ...)
> Stefan
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