Elementwise -//- first release -//- Element-wise (vectorized) function, method and operator support for iterables in python.

[Joshua Landau]

On 21 December 2011 17:51, Ian Kelly <ian.g.kelly at gmail.com> wrote:

> On Wed, Dec 21, 2011 at 9:48 AM, Joshua Landau
> <joshua.landau.ws at gmail.com> wrote:
> > functions, that before you were doing on a single item.
> > BEFORE:
> > item = foreignfunc1(item)
> > item = foreignfunc2(item)
> > item = foreignfunc3(item)
> >
> > NOW (your method):
> > item = ElementwiseProxy(item)
> > item = foreignfunc1(item)
> > item = foreignfunc2(item)
> > item = foreignfunc3(item)
> > item = list(item)
>
> Shouldn't that be:
>
> item = ElementwiseProxy(item)
> item = item.apply(foreignfunc1)
> item = item.apply(foreignfunc2)
> item = item.apply(foreignfunc3)
> item = list(item)


I was under the impression that these were meant to be interchangeable.
This is because functions are just wrappers to non-functions, really.

>>> from elementwise import ElementwiseProxy as P
>>> (lambda x:x+[1])(P([[0],[0],[0]]))
[0, 1], [0, 1], [0, 1]

If we have to use .apply, we might as well use map :P.

Note that "len" and "dir" crash.

*Here is a perfect example:*
>>> int(P(["1","2","3"]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
*TypeError: __int__ returned non-int (type ElementwiseProxy)*

It's elementwise, *but that breaks it.* An elementwise operator wouldn't
have these problems.

 > You might think your method works. But what if foreignfunc is "str"? And
> you
> > can't blacklist functions. You can't say everything works bar A, B and C.
> > What if you get: "lambda x:str(x)"? You can't blacklist that. That makes
> the
> > ElementwiseProxy version buggy and prone to unstable operation. If it's
> > consistent, fine. But it's not.
>
> I'm not sure I understand this criticism.  There is no "blacklisting"
> going on that I am aware of.  The behavior seems consistent to me:
>
> Python 2.7.1 (r271:86832, Nov 27 2010, 18:30:46) [MSC v.1500 32 bit
> (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
> >>> from elementwise import *
> >>> ewp = ElementwiseProxy(range(5))
> >>> str(ewp)
> '0, 1, 2, 3, 4'
> >>> (lambda x: str(x))(ewp)
> '0, 1, 2, 3, 4'
> >>> ewp.apply(str)
> '0', '1', '2', '3', '4'
> >>> ewp.apply(lambda x: str(x))
> '0', '1', '2', '3', '4'
>
> All of which is exactly what I expected to get.
>

Again, str(x) in this context is an outlier. It's one of the exceptions to
the rule of applying functions = elementwise.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-list/attachments/20111221/fdb9c65a/attachment-0001.html>