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

[Cesare Di Mauro]

On Lun, Apr 6, 2009 16:43, Antoine Pitrou wrote:
> Cesare Di Mauro <cesare.dimauro <at> a-tono.com> writes:
>> def f(): return ['a', ('b', 'c')] * (1 + 2 * 3)
> [...]
>>
>> With proper constant folding code, both functions can be reduced
>> to a single LOAD_CONST and a RETURN_VALUE (or, definitely, by
>> a single instruction at all with an advanced peephole optimizer).
>
> Lists are mutable, you can't optimize the creation of list literals by
> storing
> them as singleton constants.
>
> Regards
>
> Antoine.

You are right, I've mistyped the example.

def f(): return ('a', ('b', 'c')) * (1 + 2 * 3)

generates a single instruction (depending on the threshold used to limit
folding of sequences), whereas

def f(): return ['a', ('b', 'c')] * (1 + 2 * 3)

needs three.

Sorry for the mistake.

Cheers,
Cesare