performance problem in python 2.2

[Siegfried Gonzi]

Jeff Davis wrote:
> I wrote a small python program to help me solve a math problem. When I 
> tried to run it with large values, it ate all my RAM and I eventually had 
> to kill it. I tried writing the same thing in C and it used almost no RAM 
> (and had an upper limit) and finished much faster. 
> 
> Then I was talking to someone who suggested that I try perl. I have the 
> exact same algorithm in perl, and it doesn't eat my RAM, and executes much 
> more quickly (same order of magnitude as the c program). It seems almost 
> as if there's a memory leak in one of python's simple math operations, 
> because it is so much worse than the other ones I tried. 


If you need a good compiler but want not give up the convenience of a 
dynamically typed language you should take a look at Bigloo. Bigloo is a 
Scheme compiler which produces fast executables:

==
n = 1.0
p = 2.0**64
c = 1000000.0

for i in xrange(1,c+1):
	n = (n * (p - 1)) / p

print (1 - n)
==

time python bench_py.py

real 
	0m17.214s
user            0m17.190s
sys             0m0.000s


==
(module bench)

(define (sum-silly1 c)
   (let* ((n 1.0)
	 (p (expt 2.0 64.0)))
     (do ((i 1 (+ i 1)))
	((= i (+ i 1)))
       (set! n (/ (* n (- p i))
                  p)))
(print (- 1 n))))


(define (sum-silly2 c)
   (let* ((n 1.0)
	 (p (expt 2.0 64.0)))
     (do ((i 1 (+fx i 1)))
	((=fx i (+fx (flonum->fixnum c) 1)))
       (set! n (/fl (*fl n (-fl p (fixnum->flonum i)))
                  p)))
(print (- 1 n))))
	

(sum-silly1 1000000.0)

;;(sum-silly2 1000000.0)
==


bigloo -Obench bench.scm
time ./a.out

real 0m0.720s
user 0m0.690s
sys  0m0.030s


or the second version with native Bigloo floating point operations:

bigloo -Obench bench.scm
time ./a.out

real 0m0.073s
user 0m0.060s
sys  0m0.010se


==
#include <stdlib.h>
#include <stdio.h>

int main()
{
	long i,c;
         double n = 1.0;
         double p = 1.844674407370955161e+19;

         c = 1000000.0
         for (i=1;i<=c;++i)
         {
	    n = (n * (p - i)) / p;
         }

printf("%.16e\n",(1-n));
return 0;
}
==

gcc -O3 bench_c.c
time ./a.out

real 0m0.017s
user 0m0.010s
sys  0m0.000s




Bigloo is not only good at microbenchmarks it performs well on arrays 
and lists too.

I am about to release the DISLIN binding to Bigloo in a few weeks.

S. Gonzi