[Python-Dev] iterzip() (original) (raw)

Jeremy Hylton jeremy@zope.com
Mon, 29 Apr 2002 16:03:48 -0400

"TP" == Tim Peters <tim.one@comcast.net> writes:

TP> Check this out:

TP> """ from time import clock as now

TP> n = 1000000

TP> def juststore(x): TP> for i in x: x[i] = 0

TP> def justtups(x): TP> for i in x: 0,

TP> def storetups(x): TP> for i in x: x[i] = 0,

TP> def run(func): TP> x = range(n) start = now() func(x) finish = now() print TP> "%10s %6.2f" % (func.name, finish - start)

TP> run(juststore) run(justtups) run(storetups) """

TP> I get:

TP> juststore 0.93 TP> justtups 0.58 TP> storetups 7.61

TP> list.append is out of the picture here. Creating a million TP> tuples goes fast so long as they're recycled, and storing a TP> million things goes fast, but storing a million distinct tuples TP> takes very much longer. It's a Mystery to me so far. How does TP> it act on Linux?

It acts about the same on Linux.

I don't see why it's a mystery. justtups() only uses one tuple at a time; it gets re-used from the free list every time. storetups() has to (py)malloc a new tuple every stinkin' time.

Note that there's a net excess of allocations in the storetup() case, so we invoke the garbage collector every n/700 times through the loop. I've noted before that it doesn't make much sense to invoke GC unless there is at least one deallocation; you can't reclaim anything if there are no DECREFs.

Jeremy