En Sun, 18 Oct 2009 21:50:55 -0300, Carl Banks <pavlovevide...@gmail.com>
escribió:
Consider this thought experiment:
class Something(object):
def __radd__(self,other):
return other + "q"
x = ["a","b","c",Something()]
If x were passed to "".join(), it would throw an exception; but if
passed to a sum() without any special casing, it would successfully
return "abcq".
Thus there is divergence in the two behaviors, thus transparently
calling "".join() to perform the summation is a Bad Thing Indeed, a
much worse special-case behavior than throwing an exception.
Just for completeness, and in case anyone would like to try this O(n²)
process, sum(x) may be rewritten as:
x = ["a","b","c",Something()]
print reduce(operator.add, x)
which does exactly the same thing, with the same quadratic behavior as
sum(), but prints "abcq" as expected.
--
Gabriel Genellina
--
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