[Python-ideas] Fast sum() for non-numbers

[Oscar Benjamin]

On 11 July 2013 14:20, Ron Adam <ron3200 at gmail.com> wrote:
>
> On 07/11/2013 06:05 AM, Oscar Benjamin wrote:
>> On 11 July 2013 11:47, Ron Adam<ron3200 at gmail.com> wrote:
>
>    chain(iters)        # better in most cases...

I think you mean chain.from_iterable rather than chain

> I'd like to see chain as a builtin in any case.

chain.from_iterable should be the builtin not chain.

> How do you feel about adding the ability of sum to sum vectors or lists of
> values to each other?
>
> sum([[x1, y1], [x2, y2], ...])  --->  [x1+x2, y1+y2]

That's the beauty of it. sum() already sums anything you want as long
as __add__ is implemented. If I wanted to do the above with some
vectors I would probably use numpy arrays which have precisely the
__add__ method you want:

>>> import numpy as np
>>> arrays = [
...   np.array([1, 2, 3]),
...   np.array([2, 3, 4]),
...   np.array([3, 4, 5]),
... ]
>>> arrays
[array([1, 2, 3]), array([2, 3, 4]), array([3, 4, 5])]
>>> sum(arrays)
array([ 6,  9, 12])

This is possible because of the simplicity of the core algorithm in
sum() i.e. just calling 'total = total + item' in a loop. Anyone who
wants to use sum() with their own type can already do so. Earlier you
seemed to be advocating changing that by restricting the types that
sum() accepts.


Oscar