[Python-ideas] Changing optimisation level from a script

[Brett Cannon]

If people are curious as to where import makes its decision as to what
bytecode to load based on the optimization level, see
https://github.com/python/cpython/blob/ad3b9aeaab5122b22445f9120a6ccdc1987c15cc/Lib/importlib/_bootstrap_external.py#L292
 .

On Sat, 10 Sep 2016 at 04:53 Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 10 September 2016 at 03:20, Brett Cannon <brett at python.org> wrote:
> > I don't know if it's been discussed, but I have thought about it in
> context
> > of PEP 511. The problem with swapping optimization levels post-start is
> that
> > you end up with inconsistencies, e.g. asserts that depend on other
> > asserts/__debug__ to function properly. If you let people jump around you
> > potentially will break code in odd ways. Now obviously that's not
> > necessarily a reason to not allow it, but it is something to consider.
> >
> > Where this does become a potential issue in the future is if we ever
> start
> > to have optimizations that span modules, e.g. function inlining and the
> > such. We don't have support for this now, but if we ever make it easier
> to
> > do such things then the ability to change the optimization level
> > mid-execution would break assumptions or flat-out ban cross-module
> > optimizations in fear that too much code would break.
> >
> > So I'm not flat-out saying no to this idea, but there are some things to
> > consider first.
>
> We technically already have to deal with this problem, since folks can
> run compile() themselves with "optimize" set to something other than
> -1.
>
> "sys.flags.optimize" then gives the default setting used for
> "optimize" by the import system, eval, exec, etc.
>
> So if we did make this configurable, I'd suggest something along the
> lines of the other "buyer beware" settings in sys that can easily
> break the world, like setcheckinterval, setrecursionlimit,
> setswitchinterval, settrace, setprofile, and (our first PEP 8
> compliant addition), set_coroutine_wrapper.
>
> Given sys.flags.optimize already exists to read the current setting
> from Python, we'd just need "sys.set_default_optimize()" to configure
> it.
>
> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
>
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