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

[Terry Reedy]

Alexandru Moșoi wrote:
>> From: "Cesare Di Mauro" <cesare.dimauro at a-tono.com>
>> 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.
> 
> Not necessarily. For example C/C++ doesn't define the order of the
> operations inside an expression (and AFAIK neither Python)

Yes is does. Expression/Evaluation order "Python evaluates expressions 
from left to right."