[Edu-sig] Introducing Python to Engineering Students
bblais at bryant.edu
Wed Mar 12 02:34:15 CET 2008
On Mar 11, 2008, at Mar 11:8:11 PM, David MacQuigg wrote:
> At 03:12 PM 3/11/2008 -0700, Rob Malouf wrote:
>> On Mar 11, 2008, at 2:57 PM, David MacQuigg wrote:
>>> I guess what I should conclude is that when performance is
>>> important, don't bother trying to optimize Python. Go straight to
>>> C, and get 10 or 100X improvement.
>> That hasn't always been my experience. I found that using psyco and
>> numpy (along with careful profiling and optimization), I can often
>> essentially the same performance from pure Python that I can get from
>> mixed Python/C solutions, and with much less trouble.
> I agree that the Python/C interface is more trouble than it should
> be, especially for freshman engineering students and technical
> professionals who don't have time for messy programming details.
> What I would like to see is something like a simple "directive" I
> could put in my Python code to say "The following function is in
> C", and have Python set up the linkage for me.
One of the things that drew me to Python for Numerical work was Pyrex
(and now the Cython project). Here is your code in Pyrex (sans-doc
def getpts(double cx0,double cy0,double dx):
vals = 
cdef int p,i
cdef double cx,zx,zy,zx2,zy2
for p from 0<=p<100: # 100 points
cx = cx0 + p * dx # moving right x . . . . . .
zx = zy = 0.0
for i from 0<=i<1000: # 100 points
zx2 = zx*zx
zy2 = zy*zy
if (zx2 + zy2) > 4.0 : break # escape
zy = 2*zx*zy + cy0
zx = zx2 - zy2 + cx
This code gets compiled to C, and returns this unit test:
1a) Python speed = 787 points/sec
1b) C speed = 125500 points/sec
2a) Python speed = 823 points/sec
2b) C speed = 134300 points/sec
1a) Python speed = 1214 points/sec
1b) C speed = 125700 points/sec
2a) Python speed = 1287 points/sec
2b) C speed = 134500 points/sec
not too shabby! And for only putting the types of the variable into
the existing python code, and a slight modification of the for-loop
syntax, the conversion of a slow python function into a fast
extension module is trivial. One of the best things here is that for
debugging, you can put in arbitrary python code. You take the
performance hit, but you don't care during debugging, and you take it
out again for production.
bblais at bryant.edu
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