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Thu Nov 16 16:52:29 CST 2006

that the slicing behavior differs from python sequences. You might be right
that in practice aliasing doesn't cause too many problems (as long as one
sticks to arrays -- it certainly makes it harder to write code that operates
on slices of generic sequence types) -- I'd really be interested to know
whether there are cases where people have spent a long time to track down a
bug caused by the view behavior.

> with status quo on this. But, if copy-on-demand is truly efficient and
> didn't make extension writing a nightmare, I wouldn't complain about the
> change either.  I have a feeling the implementers of numarray would
> though. :-)  And talk about having to modify legacy code...

Since the vast majorities of slicing operations are currently not done to
create views that are depedently modified, the backward incompatibility might
not affect that much code. You are right though, that if Perry and the other
numarray implementors don't think that copy-on-demand could be worthwhile the
bother then its unlikely to happen.

> > forwards-compatibility). I would also suspect that this would make it
> *a
> > lot*
> > easier to get numarray (or parts of it) into the core, but this is
> just a
> > guess.
> I think the two things Guido wants for inclusion of numarray is a
> consensus from our community on what we want, and (more importantly) a
> comprehensible code base. :-)  If Numeric satisfied this 2nd condition,
> it might already be slated for inclusion...  The 1st is never easy with
> such varied opinions -- I've about concluded that Konrad and I are
> anti-particles :-) -- but I hope it will happen. 

As I said I can only guess about the politics involved, but I would think that
before a significant piece of code such as numarray is incorporated into the
core a relevant pep will be discussed in the newsgroup and that many people
will feel more confortable about incorporating something into core-python that
doesn't deviate significantly from standard behavior (i.e. doesn't
view-slice), especially if it mainly caters to a rather specialized
audience. But Guido obviously has the last word on those issues and if he
doesn't have a problem either way than either way then as long as the
community is undivided it shouldn't be an obstacle for inclusion.

I agree that division of the community might pose the most significant
problems -- MA for example *does* create copies on indexing if I'm not
mistaken and the (desirable) transition process from Numeric to numarray also
poses not insignificant difficulties and risks, especially since there now are
quite a few important projects (not least of them scipy) that are build on top
of Numeric and will have to be incorporated in the transition if numarray is
to take over. Everything seems in a bit of a limbo right now. I'm currently
working on a (fully-featured) matrix class that I'd like to work with both
Numeric and numarray (and also scipy where available) more or less
transparently for the user, which turns out to be much more difficult than I
would have thought.


Alexander Schmolck     Postgraduate Research Student
                       Department of Computer Science
                       University of Exeter
A.Schmolck at

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