Speed-up for loops

BartC bartc at freeuk.com
Sun Sep 5 19:09:47 CEST 2010

"Steven D'Aprano" <steve at REMOVE-THIS-cybersource.com.au> wrote in message 
news:4c83b425$0$28657$c3e8da3 at news.astraweb.com...
> On Sun, 05 Sep 2010 12:28:47 +0100, BartC wrote:

>> It would
>> be nice if you could directly code low-level algorithms in it without
>> relying on accelerators, and not have to wait two and a half minutes (or
>> whatever) for a simple test to complete.
> Yes, and it would be nice if my clothes washed and ironed themselves, but
> they don't.
> Somebody has to do the work. Are you volunteering to write the JIT
> compiler for CPython? Will you contribute to the PyPy project, or help
> maintain Psycho, or are you just bitching?

I've thought about it (writing an independent interpreter). But I don't know 
enough of the language, and a lot of it I don't understand (eg. OOP). 
Besides, I think the language itself deliberately makes it difficult to get 
it up to speed. Some of the reasons might be the ones set down here, in 
Chapter 2:


(Instead, I've confined my efforts to my own projects; the last interpreter 
I worked on did in fact get within a magnitude of C in performance, without 
using JIT or other fancy tricks.)

> The simple fact is that there are far more important things for Python
> developers to spend their time and effort on than optimizations like this.

I don't know, there's seem to be an awful lot of effort going into 
addressing exactly this issue (eg. PyPy, Pscyo, Unladen Swallow, 

> If such an optimization comes out of the PyPy project, I'll be cheering
> them on -- but it's a lot of effort for such a trivial gain.
> The example given by the Original Poster is contrived. Nobody sensibly
> writes an integer multiplication as a repeated addition like that, and
> any real code that would need to be put in a for loop is almost certainly
> going to be too complicated for the JIT compiler to benefit greatly. The
> loop overhead itself will almost certainly be overwhelmed by the work
> done in the loop:

OK, you're saying there's no point in reducing the loop overhead, because 
the loop body is going to be even slower.

All those compilers that offer loop unrolling are therefore wasting their 


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