On Fri, Nov 25, 2011 at 10:04 PM, Antoine Pitrou <solip...@pitrou.net> wrote: > On Fri, 25 Nov 2011 20:34:21 +1100 > Matt Joiner <anacro...@gmail.com> wrote: >> >> It's Python 3.2. I tried it for larger files and got some interesting >> results. >> >> readinto() for 10MB files, reading 10MB all at once: >> >> readinto/2.7 100 loops, best of 3: 8.6 msec per loop >> readinto/3.2 10 loops, best of 3: 29.6 msec per loop >> readinto/3.3 100 loops, best of 3: 19.5 msec per loop >> >> With 100KB chunks for the 10MB file (annotated with #): >> >> matt@stanley:~/Desktop$ for f in read bytearray_read readinto; do for >> v in 2.7 3.2 3.3; do echo -n "$f/$v "; "python$v" -m timeit -s 'import >> readinto' "readinto.$f()"; done; done >> read/2.7 100 loops, best of 3: 7.86 msec per loop # this is actually >> faster than the 10MB read >> read/3.2 10 loops, best of 3: 253 msec per loop # wtf? >> read/3.3 10 loops, best of 3: 747 msec per loop # wtf?? > > No "wtf" here, the read() loop is quadratic since you're building a > new, larger, bytes object every iteration. Python 2 has a fragile > optimization for concatenation of strings, which can avoid the > quadratic behaviour on some systems (depends on realloc() being fast).
Is there any way to bring back that optimization? a 30 to 100x slow down on probably one of the most common operations... string contatenation, is very noticeable. In python3.3, this is representing a 0.7s stall building a 10MB string. Python 2.7 did this in 0.007s. > >> readinto/2.7 100 loops, best of 3: 8.93 msec per loop >> readinto/3.2 100 loops, best of 3: 10.3 msec per loop # suddenly 3.2 >> is performing well? >> readinto/3.3 10 loops, best of 3: 20.4 msec per loop > > What if you allocate the bytearray outside of the timed function? This change makes readinto() faster for 100K chunks than the other 2 methods and clears the differences between the versions. readinto/2.7 100 loops, best of 3: 6.54 msec per loop readinto/3.2 100 loops, best of 3: 7.64 msec per loop readinto/3.3 100 loops, best of 3: 7.39 msec per loop Updated test code: http://pastebin.com/8cEYG3BD > > Regards > > Antoine. > > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/anacrolix%40gmail.com > So as I think Eli suggested, the readinto() performance issue goes away with large enough reads, I'd put down the differences to some unrelated language changes. However the performance drop on read(): Python 3.2 is 30x slower than 2.7, and 3.3 is 100x slower than 2.7. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
