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

Chris Barker chris.barker at noaa.gov
Mon Aug 4 18:25:12 CEST 2014

On Sat, Aug 2, 2014 at 1:35 PM, David Wilson <dw+python-dev at hmmz.org> wrote:

> Repeated list and str concatenation both have quadratic O(N**2) > performance, but people frequently build up strings with +

join() isn't preferable in cases where it damages readability while simultaneously providing zero or negative performance benefit, such as when concatenating a few short strings, e.g. while adding a prefix to a filename.

Good point -- I was trying to make the point about .join() vs + for strings in an intro python class last year, and made the mistake of having the students test the performance.

You need to concatenate a LOT of strings to see any difference at all -- I know that O() of algorithms is unavoidable, but between efficient python optimizations and a an apparently good memory allocator, it's really a practical non-issue.

Although it's true that join() is automatically the safer option, and especially when dealing with user supplied data, the net harm caused by teaching rote and ceremony seems far less desirable compared to fixing a trivial slowdown in a script, if that slowdown ever became apparent.

and it rarely would.

Blocking sum( some_strings) because it might have poor performance seems awfully pedantic.

As a long-time numpy user, I think sum(a_long_list_of_numbers) has pathetically bad performance, but I wouldn't block it!

-Chris

--

Christopher Barker, Ph.D. Oceanographer

Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception

Chris.Barker at noaa.gov -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20140804/0f1621d3/attachment.html>

More information about the Python-Dev mailing list