[Numpy-discussion] Possible new multiplication operators for Python

Grégory Lielens gregory.lielens@fft...
Mon Aug 18 11:55:27 CDT 2008

On Sat, 2008-08-16 at 22:03 -0700, Fernando Perez wrote:
> Hi all,
> [ please keep all replies to this only on the numpy list.  I'm cc'ing
> the scipy ones to make others aware of the topic, but do NOT reply on
> those lists so we can have an organized thread for future reference]
> In the Python-dev mailing lists, there were recently two threads
> regarding the possibility of adding to the language new multiplication
> operators (amongst others).  This would allow one to define things
> like an element-wise and a matrix product for numpy arrays, for
> example:
> http://mail.python.org/pipermail/python-dev/2008-July/081508.html
> http://mail.python.org/pipermail/python-dev/2008-July/081551.html
> It turns out that there's an old pep on this issue:
> http://www.python.org/dev/peps/pep-0225/
> which hasn't been ruled out, simply postponed.  At this point it seems
> that there is room for some discussion, and obviously the input of the
> numpy/scipy crowd would be very welcome.  I volunteered to host a BOF
> next week at scipy so we could collect feedback from those present,
> but it's important that those NOT present at the conference can
> equally voice their ideas/opinions.
> So I wanted to open this thread here to collect feedback.  We'll then
> try to have the bof next week at the conference, and I'll summarize
> everything for python-dev.  Obviously this doesn't mean that we'll get
> any changes in, but at least there's interest in discussing a topic
> that has been dear to everyone here.
> Cheers,
> f

As one of the original author behind the PEP225, I think this is an
excellent idea.
(BTW, thanks for resurrecting this old PEP :-) and considering it
useful :-) :-) ).

I think I do not need to speak to much for the PEP,  telling that I did
not change my mind should be enough ;-)...but still, I can not resist
adding a few considerations:

Demands for Elementwise operators and/or matrix product operator is
likely to resurface from time to time on Python-dev or Python-idea,
given that this is a central feature of Matlab and Matlab is a de-facto
standard when it comes to numeric-oriented interpreted languages (well,
at least in the engineering world, it is in my experience the biggest
player by far).

At the time of the original discussion on python-dev and of PEP225
redaction , I was new to Python and fresh from Matlab, and the default
behavior of elementwise-product annoyed me a lot. Since then, I have
learned to appreciate the power of numpy broadcast (Use it extensively
in my code :-) ), so the default dehavior do not annoy me anymore...
But I still feel that 2 sets of operator would be very useful
( especially in some code which implement directly heavy linear algebra
formula), the only thing where my point of view has changed is that I
now think that the Matlab way ( defining * as matrix product and .* as
elementwise product) is not necessarily the best choice, the reverse
choice is as valid...

Given the increasing success of Python as a viable alternative, I think
that settling the Elementwise operator issue is probably a good idea.
Especially as the Python 3000 transition is maybe a good time to
investigate syntax changes/extension.

> I don't think so, but given that pep 225 exists and is fully fleshed
> out, I guess it should be considered the starting point of the
> discussion for reference.  This doesn't mean that modifications to it
> can't be suggested, but that I'm assuming python-dev will want that as
> the reference point.  For something as big as this, they would
> definitely want to work off a real pep.
> Having said that, I think all ideas are fair game at this point. I
> personally would like to see it happen, but if not I'd like to see a
> final pronouncement on the matter rather than seeing pep 225 deferred
> forever.

I agree 100%. Keeping PEP 225 in limbo is the worst situation imho,
given that the discussion about elementwise operator (or matrix product)
keep showing again and again, having a final decision (even if negative)
would be better. And as I said above, I feel the timing is right for
this final decision...

Best regards,


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