[Numpy-discussion] np.insert with axis=-1

[Sebastian Berg]

On Mon, 2013-07-01 at 14:11 +0200, Félix Hartmann wrote:
> Hi all,
> 
> I recently upgraded from Numpy 1.6.2 to 1.7.1 on my Debian testing, and
> then got a bug in a program that was previously working. It turned out
> that the problem comes from the np.insert function when the argument
> `axis=-1` is given.
> 

Dang, yes, its a pretty stupid bug, exists basically the same in both
1.7 and 1.8. If you got a minute, it is because of np.rollaxis usage,
and in it there it says `axis-1` which is wrong for negative axes!

Could you create a pull request to fix that? That would be great.

- Sebastian

> Here is a minimal example:
> >>> u = np.zeros((2,3,4))
> >>> ui = np.ones((2,3))
> >>> u = np.insert(u, 1, ui, axis=-1)
> 
> The last line should be equivalent to 
> >>> u = np.insert(u, 1, ui, axis=2)
> 
> It was indeed the case in Numpy 1.6, but in 1.7.1 it raises a
> ValueError exception.
> 
> Note that the problem seems specific to axis=-1, and not to all negative
> axis values, since the following example works as expected:
> >>> u = np.zeros((2,3,4))
> >>> ui = np.ones((2,4))
> >>> u = np.insert(u, 1, ui, axis=-2)  # equivalent to axis=1
> 
> I didn't check on current master, so maybe things have changed since
> 1.7.1. If they have not, do you think a bug report would be relevant?
> 
> Cheers,
> Félix
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