[Python-Dev] pyc files, constant folding and borderline portability issues

[Paul Moore]

2009/4/7 Cesare Di Mauro <cesare.dimauro at a-tono.com>:
> The principle that I followed on doing constant folding was: "do what Python
> will do without constant folding enabled".
>
> So if Python will generate
>
> LOAD_CONST      1
> LOAD_CONST      2
> BINARY_ADD
>
> the constant folding code will simply replace them with a single
>
> LOAD_CONST      3
>
> When working with such kind of optimizations, the temptation is to
> apply them at any situation possible. For example, in other languages
> this
>
> a = b * 2 * 3
>
> will be replaced by
>
> a = b * 6
>
> In Python I can't do that, because b can be an object which overloaded
> the * operator, so it *must* be called two times, one for 2 and one for 3.
>
> That's the way I choose to implement constant folding.

That sounds sufficiently "super risk-averse" to me, so I'm in favour
of constant folding being implemented with this attitude :-)

Paul.