sum(strings)
Steve McAllister
nosp at m.needed
Fri Jun 20 12:21:28 CEST 2003
>>Since strings can be added, they should be sumable too. No? :-)
>
> Nope.
Yes ;-).
> This caused a real mess when conjoined with such issues as
> summing empty sequences and summing non-restartable iterators. The
> knot was elegantly cut by Guido, who Pronounced that sum wanted to
> be only and specifically about numbers -- and I think that, as is
> the case more often than not, he was right.
Sigma(x(i) for i from 0 to n) === x(0) + ... + x(n)
In real life, if (`+' operator)ing right term's operands _is_
defined, then the sum _is_ defined. Inside the Python matrix,
despite the fact `+' _can_ be used with strings operands, summing
them is _not_ legal. This distorsion is precisely what I found
shoking: `sum' does denote something generic and strongly (only)
related to the concept of addition.
Anyway, what about using `False' as a neater zero for the default
start value?, so that:
sum(range(3), False) # -> 3
sum((), False) # -> False
sum(('toto', 'tata')) # -> TypeError
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