[Python-ideas] Fast sum() for non-numbers - why so much worries?

[Ronald Oussoren]

On 11 Jul, 2013, at 11:07, Oscar Benjamin <oscar.j.benjamin at gmail.com> wrote:

> On 10 July 2013 19:21, Joshua Landau <joshua at landau.ws> wrote:
>> 
>> Python has previously had precedents where broken code does not get to
>> dictate the language as long as that code was very rare. This is more
>> than very rare. Additionally, Python does (unclearly, but it does do
>> so) define __iadd__ to be an inplace version of __add__, so the code
>> isn't just “broken” -- it's broken.
> 
> Although I'm quoting Joshua above, there are many people here who have
> made the erroneous assertion that __iadd__ should always be equivalent
> to __add__ and that there isn't much code that could be semantically
> affected by the proposed change.
> 
> Numpy arrays treat += differently from + in the sense that a += b
> coerces b to the same dtype as a and then adds in place whereas a + b
> uses Python style type promotion. This behaviour is by design and it
> is useful. It is also entirely appropriate (and not pathological) that
> someone would use sum() to add numpy arrays.

That, and Paul's example about using += for something else than addition,
pretty much kills the idea of using += in the implementation of sum() as that
would break to much code.

Ronald