Bulba wrote: >OK, so what projects and why would you consider >Python: >1. "clearly unsuitable"
Large-scale scientific computing projects, such as numerical weather prediction, where performance is critical. Python could be used as the "glue" but not the "guts", where Fortran 95 and C++ are more appropriate. In my tests, some posted here, there has been a significant speed differential between Fortran 95 and Python with Numeric. I don't know if using Numarray instead would change the results. Calling an extension written in C, such as Numeric, can improve performance greatly over using "pure" Python, but the speed of evaluating simple expressions can still be close to 2 orders of magnitude slower. Here is an example that computes (1) sum(x) (2) sum(x**2) (3) sum((x-0.5)**2) for 1E7 uniformly distributed random numbers. # Python from RandomArray import random from time import time from Numeric import sum n = 10000000 half = 0.5 x = random(n) for iopt in range(1,4): t1 = time() if (iopt == 1): xsum = sum(x) elif (iopt == 2): xsum = sum(x**2) elif (iopt == 3): xsum = sum((x-half)**2) t2 = time() print iopt,xsum,t2-t1 ! Fortran 95 program xsum_power implicit none integer, parameter :: n = 10000000 real(kind=8) :: x(n),xsum,t1,t2 real , parameter :: half = 0.5 integer :: iopt iopt = 1 call random_seed() call random_number(x) do iopt=1,3 call cpu_time(t1) select case (iopt) case (1) ; xsum = sum(x) case (2) ; xsum = sum(x**2) case (3) ; xsum = sum((x-half)**2) end select call cpu_time(t2) write (*,"(i4,100f16.6)") iopt,xsum,t2-t1 end do end program xsum_power The approximate times taken in seconds, in Python and Fortran, are task Fortran Python sum(x) 0.05 0.1 sum(x**2) 0.05 2.4 sum((x-0.5)**2) 0.05 3.2 In the Fortran code, essentially all the time is spent accessing the array elements. Powers and subtractions in array operations seem to be free in Fortran but very expensive in Python with Numeric. Not wanting to be guilty of "premature optimization", I did not try to make either code more efficient than my first attempt. The Fortran compiler is Compaq Visual Fortran 6.6c, and the Python used is 2.2. -- http://mail.python.org/mailman/listinfo/python-list
