loops - Python nested looping Idiom

Question

I often find myself doing this:

for x in range(x_size):
    for y in range(y_size):
        for z in range(z_size):
            pass # do something here

Is there a more concise way to do this in Python? I am thinking of something along the lines of

for x, z, y in ... ? :

Answer 1

You can use itertools.product:

>>> for x,y,z in itertools.product(range(2), range(2), range(3)):
...     print x,y,z
... 
0 0 0
0 0 1
0 0 2
0 1 0
0 1 1
0 1 2
1 0 0
1 0 1
1 0 2
1 1 0
1 1 1
1 1 2

Answer 2

If you've got numpy as a dependency already, numpy.ndindex will do the trick ...

>>> for x,y,z in np.ndindex(2,2,2):
...     print x,y,z
... 
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1

Answer 3

Use itertools.product():

import itertools
for x, y, z in itertools.product(range(x_size), range(y_size), range(z_size)):
    pass # do something here

From the docs:

Cartesian product of input iterables.

Equivalent to nested for-loops in a generator expression.
...

Answer 4

It depends on what is inside the loop. If dealing with lists, you may be able to use a list comprehension

For the more general case, see this post on itertools.