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[Python-Dev] PEP 488: elimination of PYO files

Brett Cannon brett at python.org
Fri Mar 6 19:11:19 CET 2015 
On Fri, Mar 6, 2015 at 1:03 PM Mark Shannon <mark at hotpy.org> wrote:

>
> On 06/03/15 16:34, Brett Cannon wrote:
> > Over on the import-sig I proposed eliminating the concept of .pyo files
> > since they only signify that /some/ optimization took place, not
> > /what/ optimizations took place. Everyone on the SIG was positive with
> > the idea so I wrote a PEP, got positive feedback from the SIG again, and
> > so now I present to you PEP 488 for discussion.
> >
> [snip]
>
> Historically -O and -OO have been the antithesis of optimisation, they
> change the behaviour of the program with no noticeable effect on
> performance.
> If a change is to be made, why not just drop .pyo files and be done with
> it?
>

I disagree with your premise that .pyo files don't have a noticeable effect
on performance. If you don't use asserts a lot then there is no effect, but
if you use them heavily or have them perform expensive calculations then
there is an impact. And the dropping of docstrings does have an impact on
memory usage when you use Python at scale.

You're also assuming that we will never develop an AST optimizer that will
go beyond what the peepholer can do based on raw bytecode, or something
that involves a bit of calculation and thus something you wouldn't want to
do at startup.


>
> Any worthwhile optimisation needs to be done at runtime or involve much
> more than tweaking bytecode.
>

I disagree again. If you do something like whole program analysis and want
to use that to optimize something, you will surface that through bytecode
and not editing the source. So while you are doing "much more than tweaking
bytecode" externally to Python, you still have to surface to the
interpreter through bytecode.
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