On Fri, 25 Nov 2011 22:37:49 +1100 Matt Joiner <anacro...@gmail.com> wrote: > 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.
Well, extending a bytearray() (as you saw yourself) is the proper solution in such cases. Note that you probably won't see a difference when concatenating very small strings. It would be interesting if you could run the same benchmarks on other OSes (Windows or OS X, for example). 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/archive%40mail-archive.com
