[Numpy-discussion] Questions about the array interface.

[Chris Barker]

Scott Gilbert wrote:
 > I think __array_version__ (or __array_protocol__?) is the
 > better choice.  How about have it optional and default to 1?  If it's
 > present and greater than 1 then it means there is something new going 
on...

Again, I'm uncomfortable with something that I have to check being 
optional. If it is, we're encouraging people to not check it, and that' 
a recipe for bugs later on down the road.

 > Everyone seems to think that an offset is so weird.  I haven't looked at
 > the internals of Numeric/scipy.base in a while so maybe it doesn't apply
 > there.  However, if you subscript an array and return a view to the data,
 > you need an offset or you need to create a new buffer that encodes the
 > offset for you.

 > I guess all I'm saying is that I wouldn't assume the offset is zero...

Good point. All the more reason to have the offset be mandatory.

 > The fact that a lot of these attributes are optional should be hidden in
 > helper functions like those in Travis's array_interface.py module, or a
 > C/C++ include file (with inline functions).

Yes, if there is a C/C++ version of all these helper functions, I'll be 
a lot happier. And you're right, the same information should not be 
encoded in two places, so my "iscontiguous" attribute should be a helper 
function or maybe a method.

 > In a short while, you shouldn't have to check any __array_metadata__
 > attributes directly.  There should even be a helper function for getting
 > the array elements.

Cool. How would that work? A C++ iterator? I"m thinking not, as this is 
all C, no?

 > It wouldn't be a horrible mistake to have all the attributes be 
mandatory,
 > but it doesn't get array consumes any benefit that they can't get from a
 > well written helper library, and it does add some burden to array
 > producers.

Hardly any. I'm assuming that there will be a base_array class that can 
be used as a base class or mixin, so it wouldn't be any work at all to 
have a full set of attributes with defaults. It would take up a little 
bit of memory. I'm assuming that the whole point of this is to support 
large datasets, but maybe that isn't a valid assumption, After all, 
small array support has turned out to be very important for Numeric.

As a rule of thumb, I think there will be consumers of arrays that 
producers, so I'd rather make it easy on the consumers that the 
producers, if we need to make such a trade off. Maybe I'm biased, 
because I'm a consumer.

-Chris

-- 
Christopher Barker, Ph.D.
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