performance of Nested for loops

[querypk]

Is there a better way to code nested for loops as far as performance is
concerned.

what better way can we write to improve the speed.
for example:
N=10000
for i in range(N):
for j in range(N):
do_job1
for j in range(N):
do_job2

 

[Charles Krug]

Is there a better way to code nested for loops as far as performance is
concerned.

what better way can we write to improve the speed.
for example:
N=10000
for i in range(N):
for j in range(N):
do_job1
for j in range(N):
do_job2

What do you see when you profile the code?

Premature Optimization is the root of all manner of evil and all that
good stuff.

 

[Larry Bates]

You can use xrange(N) that way Python doesn't have
to build the 10000 item lists 20000 times. Other than
that one would need to know why you would call do_job1
and do_job2 10000 times each inside a 10000 iteration
loop. Most VERY large performance gains are due to
better algorithms not code optimization.

Larry Bates

 

[Andrew Dalke]

Is there a better way to code nested for loops as far as performance is
concerned.

what better way can we write to improve the speed.
for example:
N=10000
for i in range(N):
for j in range(N):
do_job1
for j in range(N):
do_job2

For this case compute the range once

range_10000 = range(10000)
for i in range_10000:
for j in range_10000:
do_job1()
for j in range_10000:
do_job2()

Using xrange(10000) may be faster but you would need to test
that out for your case.

Andrew
(e-mail address removed)