On Mar 15, 2005, at 01:16, Tim Peters wrote:
[Eric Nieuwland]Perhaps the second argument should not be optional to emphasise this. After all, there's much more to sum() than numbers.
[Greg Ewing]I think practicality beats purity here. Using it on numbers is surely an extremely common case.
I'd personally be delighted if sum() never worked on anything other than numbers. That makes it easy to understand, easy to document, easy to remember, obvious at first sight, and straightforward to implement. Everything a framework isn't, but it's not a bad thing to have *something* that actually means exactly what it looks like it says <0.5 wink>.
I'm reasonably often using sum on lists of datetime.timedelta instances, "durations", which ARE summable just like numbers even though they aren't numbers. I believe everything else for which I've used sum in production code DOES come under the general concept of "numbers", in particular X+0 == X. Unfortunately, this equation doesn't hold when X is a timedelta, as X+0 raises an exception then.
Alex
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