[Python-Dev] collections module
Guido van Rossum
guido at python.org
Tue Jan 13 12:14:22 EST 2004
> > Just in case nobody had thought of it before, couldn't the realloc()
> > call be avoided when roundupsize(oldsize) == roundupsize(newsize)???
> Followup: it's not quite that easy, because (at least) PyList_New(int size)
> can create a list whose allocated size hasn't been rounded up.
> If I "fix" that, then it's possible to get away with just one roundupsize()
> call on most list.insert() calls (including list.append()), while avoiding
> the realloc() call too. Patch attached.
> I timed it like so:
> def punchit():
> from time import clock as now
> a = 
> push = a.append
> start = now()
> for i in xrange(1000000):
> finish = now()
> return finish - start
> for i in range(10):
> print punchit()
> and got these elapsed times (this is Windows, so this is elapsed wall-clock
> before after
> ------------- --------------
> 1.05227710823 1.02203188119
> 1.05532442716 0.569660068053
> 1.05461539751 0.568627533147
> 1.0564449622 0.569336562799
> 1.05964146231 0.573247959235
> 1.05679528655 0.568503494862
> 1.05569402772 0.569745553898
> 1.05383177727 0.569499991619
> 1.05528000805 0.569163914916
> 1.05636618113 0.570356526258
> So pretty consistent here, apart from the glitch on the first "after" run,
> and about an 80% speedup.
> Yawn <wink>.
> If someone wants to run with this, be my guest. There may be other holes
> (c.f. PyList_New above), and it could sure use a comment about why it's
> correct (if it in fact is <0.9 wink>).
Awesome! We need timing results on some other platforms (Linux,
--Guido van Rossum (home page: http://www.python.org/~guido/)
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