[Python-ideas] Disable all peephole optimizations

[Eric Snow]

On Thu, May 22, 2014 at 11:59 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> On Thu, May 22, 2014 at 03:41:31PM +0000, Steve Dower wrote:
>
>> Why not move the existing optimisation into -O mode and put future
>> optimisations in there too? It may just start having enough value that
>> people switch to using it.
>
> I just had the same idea, you beat me to it.

Same here.  More concretely:

-O0 -- no optmizations at all
-O1 -- level 1 optimizations (current peephole optmizations), asserts disabled
-O2 -- level 2 optimizations (currently nothing extra)
-O3 -- ...
-ONs or -X nodocstrings or -X compact or --compact or --nodocstrings
-- remove docstrings (for space savings)
--debug or -X debug -- sets __debug__ to True (also implies -O0)

Compatibility (keeping the current behavior):
Default: -O<max> + __debug__ = True (deprecate setting __debug__ to True?)
-O -- same as -O<max>
-OO -- same as -O<max>s (deprecate)

Having the current optimizations correspond to -O1 makes sense in that
we don't have anything more granular.  However, if more optimizations
were added I'd expect them to fall under a higher optimization level.

Adding a new option just for docstrings/compact seems like a I waste
so I like Stefan's idea of optionally appending "s" (for space) onto
the -O option.

As Barry noted, we would also build on PEPs 3147/3149 to add a tag for
the optmization level, etc.  The default mode would keep the current
cache tag and -O/-OO would likewise stay the same (with the .pyo
suffix).

> * The double -OO switch should be deprecated, for eventual removal
>   in the very distant future. (4.0? 5.0?)

Good idea.

> * Instead, a separate switch for removing docstrings can be added,
>   to support implementations in low-memory devices or other
>   constrained situations.

Also a good idea.

> This will make Python's compilation model a little more familiar to
> people coming from other languages.  It will make -O more attractive,
> instead of being viewed by some as a waste of effort, and ensure that by
> default there are no tricks played with byte-code.

+1

-eric