list.clear() missing?!?

[Serge Orlov]

Martin v. Löwis wrote:
> Felipe Almeida Lessa wrote:
> > I love benchmarks, so as I was testing the options, I saw something very
> > strange:
> >
> > $ python2.4 -mtimeit 'x = range(100000); '
> > 100 loops, best of 3: 6.7 msec per loop
> > $ python2.4 -mtimeit 'x = range(100000); del x[:]'
> > 100 loops, best of 3: 6.35 msec per loop
> > $ python2.4 -mtimeit 'x = range(100000); x[:] = []'
> > 100 loops, best of 3: 6.36 msec per loop
> > $ python2.4 -mtimeit 'x = range(100000); del x'
> > 100 loops, best of 3: 6.46 msec per loop
> >
> > Why the first benchmark is the slowest? I don't get it... could someone
> > test this, too?
>
> In the first benchmark, you need space for two lists: the old one and
> the new one; the other benchmarks you need only a single block of
> memory (*). Concluding from here gets difficult - you would have to study
> the malloc implementation to find out whether it works better in one
> case over the other. Could also be an issue of processor cache: one
> may fit into the cache, but the other may not.

Addition to the previous message. Now I follow you :) There are indeed
two arrays and cache seems to be the second reason for slowdown, but
iterating backwards is also contributing to slowdown.