Quoting Laszlo Nagy <[EMAIL PROTECTED]>:
> [EMAIL PROTECTED] wrote:
> > Empty Python lists [] don't know the type of the items it will
> > contain, so this sounds strange:
> >
> >
> >>>> sum([])
> >>>>
> > 0
> >
> > Because that [] may be an empty sequence of someobject:
> >
>
> You are right in that sum could be used to sum arbitrary objects.
> However, in 99.99% of the cases, you will be summing numerical values.
> When adding real numbers, the neutral element is zero. ( X + 0 = X) It
> is very logical to return zero for empty sequences.
Even better:
help(sum) shows
===
sum(...)
sum(sequence, start=0) -> value
Returns the sum of a sequence of numbers (NOT strings) plus the value
of parameter 'start'. When the sequence is empty, returns start.
===
so the fact that sum([]) returns zero is just because the start value is zero...
sum([],object()) would return an object().
BTW, the original code:
>>> sum(s for s in ["a", "b"] if len(s) > 2)
wouldn't work anyway... it seems that sum doesn't like to sum strings:
>>> sum(['a','b'],'')
<type 'exceptions.TypeError'>: sum() can't sum strings [use ''.join(seq)
instead]
Cheers,
--
Luis Zarrabeitia
Facultad de Matemática y Computación, UH
http://profesores.matcom.uh.cu/~kyrie
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