[Python-ideas] Disable all peephole optimizations

[Ned Batchelder]

On 5/23/14 1:22 PM, Guido van Rossum wrote:
> On Fri, May 23, 2014 at 10:17 AM, Eric Snow 
> <ericsnowcurrently at gmail.com <mailto:ericsnowcurrently at gmail.com>> wrote:
>
>     On Fri, May 23, 2014 at 10:49 AM, Guido van Rossum
>     <guido at python.org <mailto:guido at python.org>> wrote:
>     > Looking at my own (frequent) use of coverage.py, I would be
>     totally fine if
>     > disabling peephole optimization only affected my app's code, and
>     kept using
>     > the precompiled stdlib. (How exactly this would work is left as
>     an exercise
>     > for the reader.)
>
>     Would it be a problem if .pyc files weren't generated or used (a la -B
>     or PYTHONDONTWRITEBYTECODE) when you ran coverage?
>
>
> In first approximation that would probably be okay, although it would 
> make coverage even slower. I was envisioning something where it would 
> still use, but not write, pyc files for the stdlib or site-packages, 
> because the code in whose coverage I am interested is puny compared to 
> the stdlib code it imports.

I was concerned about losing any time in test suites that are already 
considered too slow.  But I tried to do some controlled measurements of 
these scenarios, and found the worst case (no .pyc available, and none 
written) was only 2.8% slower than full .pyc files available.  When I 
tried to measure stdlib .pyc's available, and no .pyc's for my code, the 
results were actually very slightly faster than the typical case.  I 
think this points to the difficult in controlling all the variables!

In any case, it seems that the penalty for avoiding the .pyc files is 
not burdensome.
>
> -- 
> --Guido van Rossum (python.org/~guido <http://python.org/%7Eguido>)
>
>
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