In python is there an easier way to write 6 nested for loops?

Question

This problem has been getting at me for a while now. Is there an easier way to write nested for loops in python? For example if my code went something like this

Answer 1

Assuming each loop has some sort of independent meaning, break them out into named functions:

def do_tigers():
    for x in range(3):
        print something

def do_lions():
    do_lionesses()
    for x in range(3):
        do_tigers()

def do_penguins():
    for x in range(3):
        do_lions()

..etc.

I could perhaps have chosen better names. 8-)

Answer 2

This is fairly common when looping over multidimensional spaces. My solution is:

xy_grid = [(x, y) for x in range(3) for y in range(3)]

for x, y in xy_grid:
    # do something
    for x1, y1 in xy_grid:
        # do something else

Answer 3

From your code it looks like you want to perform an operation with every possible pair of points where x and y are in the range 0..2.

To do that:

for x1,y1,x2,y2 in itertools.product(range(3), repeat=4):
    do_something_with_two_points(x1,y1,2,y2)

The operation do_something_with_two_points will be called 81 times - once for every possible combination of points.

Answer 4

If you're frequently iterating over a Cartesian product like in your example, you might want to investigate Python 2.6's itertools.product -- or write your own if you're in an earlier Python.

from itertools import product
for y, x in product(range(3), repeat=2):
  do_something()
  for y1, x1 in product(range(3), repeat=2):
    do_something_else()

Answer 5

Technically, you could use itertools.product to get a cartesian product of N sequences, and iterate over that:

 for y, x, y1, x1 in itertools.product(range(3), repeat=4):
   do_something_else()

But I don't think that actually wins you anything readability-wise.

Answer 6

That way looks pretty straightforward and easy. Are you are saying you want to generalize to multiple layers of loops.... can you give a real-life example?

Another option I could think of would be to use a function to generate the parameters and then just apply them in a loop

def generate_params(n):
    return itertools.product(range(n), range(n))

for x,y in generate_params(3):
    do_something()