[Python-Dev] sum(...) limitation

Nikolaus Rath Nikolaus at rath.org
Wed Aug 13 04:48:34 CEST 2014

Chris Barker <chris.barker at noaa.gov> writes:
> What I fail to see is why it's better to raise an exception and point users
> to a better way, than to simply provide an optimization so that it's a mute
> issue.
> The only justification offered here is that will teach people that summing
> strings (and some other objects?) is order(N^2) and a bad idea. But:
> a) Python's primary purpose is practical, not pedagogical (not that it
> isn't great for that)
> b) I doubt any naive users learn anything other than "I can't use sum() for
> strings, I should use "".join()". Will they make the leap to "I shouldn't
> use string concatenation in a loop, either"? Oh, wait, you can use string
> concatenation in a loop -- that's been optimized. So will they learn: "some
> types of object shave poor performance with repeated concatenation and
> shouldn't be used with sum(). So If I write such a class, and want to sum
> them up, I'll need to write an optimized version of that code"?
> I submit that no naive user is going to get any closer to a proper
> understanding of algorithmic Order behavior from this small hint. Which
> leaves no reason to prefer an Exception to an optimization.
> One other point: perhaps this will lead a naive user into thinking --
> "sum() raises an exception if I try to use it inefficiently, so it must be
> OK to use for anything that doesn't raise an exception" -- that would be a
> bad lesson to mis-learn....

AOL to that.


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