[Python-Dev] Anyone still using Python 2.5?

Tim Wintle timwintle at gmail.com
Thu Dec 22 12:05:09 CET 2011

On Thu, 2011-12-22 at 10:56 +0100, Antoine Pitrou wrote:
> On Thu, 22 Dec 2011 09:44:32 +0000
> Tim Wintle <timwintle at gmail.com> wrote:
> > 
> > 2.5 apps are the speed-critical ones. Our tests showed the performance
> > was different enough between 2.5 and 2.6 for me to not update.
> Really? Where's the regression?

I'm not certain - IIRC there were several nice optimisations in 2.6, and
I wasn't expecting that when I first looked.

I was running code designed for 2.5 under 2.6, so it's likely that with
sufficient tweaking for 2.6 I might not have the same result. I tested
this specific code with the python builds we have in production, not
general python code - I don't mean this as a recommendation that anyone
else assume 2.5 is faster for them.

I suspect that Stefan's comments about newly added features without the
optimisation in python3 might be partially true, but having the extra
code to support them (while not using them) might also be part of the
cause - ceval.c had over 1K line changes between r25 and r26, including
cases for new opcodes, and new opcode predictions etc - it's possible
that my code just happens to not follow the most optimal paths.

I'm talking about a slow-down of under 10%, but enough that I couldn't
justify moving these apps to 2.6 at the time for economic reasons, and
pypy would be the main incentive to move this to 2.7.


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