Using D

[Ali Çehreli via Digitalmars-d]

On 07/11/2014 09:53 AM, simendsjo wrote:

 > On 07/11/2014 06:28 PM, Russel Winder via Digitalmars-d wrote:
 >> On Fri, 2014-07-11 at 17:43 +0200, simendsjo via Digitalmars-d wrote:
 >> […]
 >>> A little anecdote.. I once got a 20% speed increase in Python by
 >>> "moving" a variable instantiation outside a tight loop.
 >>>    i = 0
 >>>    # loop here
 >>>      i = something
 >>>
 >>> rather than
 >>>    # loop here
 >>>      i = something
 >>
 >> This is interesting. I can believe there is some performance benefit,
 >> but I am not sure I believe 20% improvement. If you can send me the code
 >> you were using, I would like to do some benchmarking on this.
 >
 > Yes, I was very perplexed when I was profiling and finally found the
 > main offender. Unfortunately I don't have the code - it was a project
 > done for a past employer back in 2006/2007 (Python 2.4 IIRC).
 >
 >>> The compiler wasn't smart enough to do this.
 >>
 >> The Python compiler cannot and will never be able to do any such thing.
 >> Indeed if it did any such thing, it would be an error since it
 >> significantly changes the semantics of the program. Thus not doing this
 >> is not the fault of the compiler.  The fact that you were able to do
 >> this and it appeared to give you the same results just means that the
 >> change in program semantics did not affect your computation. Which is
 >> good, but not something the compiler could determine.
 >
 > I think of this as a fault in the compiler. It was quite obvious (to me)
 > that nothing else relied on the value so the value didn't have to be
 > created on each iteration.

Can that 'i = something' expression be monkey-patched in Python? If so, 
it could have side-effects to make the program change semantics like 
Russel Winder means.

Ali