[Numpy-discussion] what would you expect A[none] to do?

[Benjamin Root]

TBH, I wouldn't have expected it to work, but now that I see it, it does
make some sense. I would have thought that it would error out as being
ambiguous (prepend? append?). I have always used ellipses to make it
explicit where the new axis should go. But, thinking in terms of how
regular indexing works, I guess it isn't all that ambiguous.

Ben Root

On Thu, Dec 31, 2015 at 11:56 AM, Joe Kington <joferkington at gmail.com>
wrote:

> Slicing with None adds a new dimension.  It's a common paradigm, though
> usually you'd use A[np.newaxis] or A[np.newaxis, ...] instead for
> readibility.   (np.newaxis is None, but it's a lot more readable)
>
> There's a good argument to be made that slicing with a single None
> shouldn't add a new axis, and only the more readable forms like A[None, :],
> A[..., None], etc should.
>
> However, that would rather seriously break backwards compatibility.
> There's a fair amount of existing code that assumes "A[None]" prepends a
> new axis.
>
> On Thu, Dec 31, 2015 at 10:36 AM, Neal Becker <ndbecker2 at gmail.com> wrote:
>
>> Neal Becker wrote:
>>
>> > In my case, what it does is:
>> >
>> > A.shape = (5760,)
>> > A[none] -> (1, 5760)
>> >
>> > In my case, use of none here is just a mistake.  But why would you want
>> > this to be accepted at all, and how should it be interpreted?
>>
>> Actually, in my particular case, if it just acted as a noop, returning the
>> original array, that would have been perfect.  No idea if that's a good
>> result in general.
>>
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