[Python-Dev] PATCH submitted: Speed up + for string concatenation, now as fast as "".join(x) idiom
larry at hastings.org
Thu Oct 5 23:23:08 CEST 2006
Gregory P. Smith wrote:
> have you run any generic benchmarks such as pystone to get a better
> idea of what the net effect on "typical" python code is?
I hadn't, but I'm happy to. On my machine (a fire-breathing Athlon 64
x2 4400+), best of three runs:
Python 2.5 release:
Pystone(1.1) time for 50000 passes = 1.01757
This machine benchmarks at 49136.8 pystones/second
Python 2.5 concat:
Pystone(1.1) time for 50000 passes = 0.963191
This machine benchmarks at 51910.8 pystones/second
I'm surprised by this; I had expected it to be slightly *slower*, not
the other way 'round. I'm not sure why this is. A cursory glance at
pystone.py doesn't reveal any string concatenation using +, so I doubt
it's benefiting from my speedup. And I didn't change the optimization
flags when I compiled Python, so that should be the same.
Josiah Carlson wrote:
> Regardless of "nicer to read", I would just point out that Guido has
> stated that Python will not have strings implemented as trees.
I suspect it was more a caution that Python wouldn't *permanently* store
strings as "ropes". In my patch, the rope only exists until someone
asks for the string's value, at which point the tree is rendered and
dereferenced. From that point on the object is exactly like a normal
PyStringObject to the external viewer.
But you and I are, as I believe the saying goes, "channeling Guido
(badly)". Perhaps some adult supervision will intervene soon and make
its opinions known.
For what it's worth, I've realized two things I want to change about my
* I left in a couple of /* lch */ comments I used during development
as markers to find my own code. Whoops; I'll strip those out.
* I realized that, because of struct packing, all PyStringObjects are
currently wasting an average of two bytes apiece. (As in, that's
something Python 2.5 does, not something added by my code.) I'll change
my patch so strings are allocated more precisely. If my string
concatenation patch is declined, I'll be sure to submit this patch
I'll try to submit an updated patch today.
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