[Numpy-discussion] Add an axis argument to generalized ufuncs?

Stephan Hoyer shoyer at gmail.com
Sun Oct 19 15:52:03 EDT 2014


On Sun, Oct 19, 2014 at 6:43 AM, Nathaniel Smith <njs at pobox.com> wrote:

> I feel strongly that we should come up with a syntax that is
>
unambiguous even *without* looking at the gufunc signature. It's easy
> for the computer to disambiguate stuff like this, but it'd be cruel to
> ask people trying to skim through code to work out the signature and
> then simulate the disambiguation algorithm in their head.
>

Since code speaks stronger than mere words, here is a notebook showing my
disambiguation algorithm:
http://nbviewer.ipython.org/gist/shoyer/7740d32850084261d870

I don't think this is so cruel, but I agree that the logic is more complex
than ideal:

"If the axis argument is a sequence with length equal to the number of
variables with axis specifications in the gufunc signature, then each
element is taken to specify the axis for each corresponding variable.
Otherwise, if the gufunc has only one variable with a core dimension, the
entire axis argument is taken to refer to only that variable."


> Notice in my suggestion above there are two different kwargs, "axis" and
> "axes".


Ah, I missed that. That's actually pretty elegant, so +1 from me. My only
ask then would be that we allow for "axis" to also be a sequence of
integers, in which case they are also used to specify the axis for the
single variable, e.g., axis=(1, 2) translates to axes=[(1, 2)]. This would
allow for using the axis argument in the same way as it works on
ufunc.reduce already. I don't think distinguishing cases for "integer" vs
"tuple of integers" is too complex.
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