[Python-ideas] Changing optimisation level from a script

[Andrew Svetlov]

There are also peephole optimization.
Removing it may prevent false positives for coverage tool
http://bugs.python.org/issue2506

On Sat, Sep 10, 2016 at 4:01 AM Steven D'Aprano <steve at pearwood.info> wrote:

> On Sat, Sep 10, 2016 at 10:04:46AM +1000, Damien George wrote:
>
> > I guess my main question to this list is: if CPython were to add a
> > function to change the optimisation level at runtime, what would it
> > look like?
>
> I don't think it would look like sys.optimize(flag). At the very least,
> it would have to take *at least* three values:
>
> - no optimizations (the default)
> - remove asserts (-O)
> - remove asserts and docstrings (-OO)
>
> but even that is very limiting. Why can't I keep asserts, which may be
> useful and important in running code, but remove docstrings, which
> mostly are used interactively? I think the idea of "optimization levels"
> has reached its use-by date and we should start considering separate
> flags for each individual optimization.
>
> In particular, I expect that some time soon somebody will propose at
> least one more optimization:
>
> - remove annotations
>
> and I seem to recall somebody requesting the ability to turn off
> constant folding, although I don't remember why. I can easily imagine
> Python implementations offering flags to control more complex/risky
> optimizations:
>
> - resolve built-in names at compile-time[1]
> - inline small functions
> - unroll loops
>
> etc. Victor Stinner is (I think) working on bringing some of these to
> CPython, and it seems to me that if they are to be under any
> user-control at all, a simple optimization level counter is not going to
> be sufficient. We're going to need a set of flags.
>
> But it seems to me that the ability to change optimizations at runtime
> would be rather confusing. Shouldn't optimizations, or at least some of
> them, apply on a per-module basis rather than globally?
>
> I don't even know how to reason about code optimizations if any function
> I run might have changed the optimization level without my knowledge. So
> I think this is a very dubious idea.
>
>
>
>
>
>
> [1] Yes, I know that will change the semantics of Python code.
>
>
> --
> Steve
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-- 
Thanks,
Andrew Svetlov
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