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@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@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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