Hi Lennart,
Sent from my Ei4Steve
On Feb 13, 2013, at 8:42, Lennart Regebro <rege...@gmail.com> wrote:
>> Something is needed - a patch for PyPy or for the documentation I guess.
>
> Not arguing that it wouldn't be good, but I disagree that it is needed.
>
> This is only an issue when you, as in your proof, have a loop that
> does concatenation. This is usually when looping over a list of
> strings that should be concatenated together. Doing so in a loop with
> concatenation may be the natural way for people new to Python, but the
> "natural" way to do it in Python is with a ''.join() call.
>
> This:
>
> s = ''.join(('X' for x in xrange(x)))
>
> Is more than twice as fast in Python 2.7 than your example. It is in
> fact also slower in PyPy 1.9 than Python 2.7, but only with a factor
> of two:
>
> Python 2.7:
> time for 10000000 concats = 0.887
> Pypy 1.9:
> time for 10000000 concats = 1.600
>
> (And of course s = 'X'* x takes only a bout a hundredth of the time,
> but that's cheating. ;-)
>
> //Lennart
This all does not really concern me, as long as it roughly has the same order
of magnitude, or better the same big Oh.
I'm not concerned by a constant factor.
I'm concerned by a freezing machine that suddenly gets 10000 times slower
because the algorithms never explicitly state their algorithmic complexity.
( I think I said this too often, today?)
As a side note:
Something similar happened to me when somebody used "range" in Python3.3.
He ran the same code on Python 2.7.
with a crazy effect of having to re-boot:
Range() on 2.7 with arguments from some arbitrary input file. A newbie error
that was hard to understand, because
he was tought thinking 'xrange' when writing 'range'. Hard for me to understand
because I am no longer able to make these errors at all, or even expect them.
Cheers - Chris
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