Avoiding nested for loops

Question

I am trying to do some parameter testing on another code using python. I need to test 6 independent parameters, but I need all of the possible combinations of them.

Each parameter has a minimum, a maximum, and a step value that needs to be passed to it. The first easy solution that popped into my head was a nested for loop structure that looked horrific, like this:

for var1 in xrange(min1,max1,step1):
    for var2 in xrange(min2,max2,step2):
        ...
            ...
                ...
                    for var6 in xrange(min6,max6,step6):
                        '''
                        Do something and be icky in the process due
                        to being in the middle of six nested for loops
                        '''

I decided, no! This shall not stand. So I've been trying to work out a way to do this recursively, or at the very least, not nested six times. I can't really come up with a good scheme to do so. The biggest obstacle for me is that each variable has a different min, max, and step value.

My thoughts so far aren't very helpful. I keep trying to make some recursive function work, but I just can't figure it out without nesting more for loops within the function. I've seen a lot of reference to itertools.product on here, but I can't quite figure out how to make that work either.

Edit: What I'm doing is creating a directory named after the combination of the parameters, writing a file with those parameters, running another code with this file, and analyzing the output from that code. I am doing nothing in literally any of the for loops except for the final one. A lot of the parameters only have 2 values, some have 10, others have 3... it just kind of varies.

Answer 1

Here's how to use product:

x1 = xrange(min1,max1,step1)
x2 = xrange(min2,max2,step2)
x3 = xrange(min3,max3,step3)
...

for v1, v2, v3, v4, v5, v6 in itertools.product(x1, x2, x3, x4, x5, x6):
    icky_thing(....)

or a bit more compactly:

ranges = [
    xrange(min1,max1,step1),
    xrange(min2,max2,step2),
    xrange(min3,max3,step3),
    ...
]

for v1, v2, v3, v4, v5, v6 in itertools.product(*ranges):
    icky_thing(....)

Answer 2

You can probably use itertools.product: http://docs.python.org/library/itertools.html#itertools.product .

Something like

for var1, var2 in itertools.product(xrange(min1, max1, step1), xrange(min2, max2, step2)):
    # stuff

. . . only with all six vars in there.

Answer 3

you can use multiprocessing and itertools.product to speed up and simplify your code

import itertools
from multiprocessing import Pool

ranges = [
    range(min1,max1,step1),
    range(min2,max2,step2),
    range(min3,max3,step3),
    ...
]

with Pool(os.cpu_count()-2) as p:
    result = p.map(your_op_func, itertools.product(*ranges))

1. multiprocessing can speed up your task (because it's mutex task)
2. itertools.product can help you get combinations through a more effectively way