[FIXED] How can I make a for-loop pyramid more concise in Python?

Issue

In solid mechanics, I often use Python and write code that looks like the following:

for i in range(3):
    for j in range(3):
        for k in range(3):
            for l in range(3):
                # do stuff

I do this really often that I start to wonder whether there is a more concise way to do this. The drawback of the current code is: if I comply with PEP8, then I cannot exceed the 79-character-limit per line, and there is not too much space left, especially if this is again in a function of a class.

Solution

By using nested for-loops you're basically trying to create what's known as the (Cartesian) product of the input iterables, which is what the product function, from itertools module, is for.

>>> list(product(range(3),repeat=4))
[(0, 0, 0, 0), (0, 0, 0, 1), (0, 0, 0, 2), (0, 0, 1, 0), (0, 0, 1, 1),
 (0, 0, 1, 2), (0, 0, 2, 0), (0, 0, 2, 1), (0, 0, 2, 2), (0, 1, 0, 0),
...

And in your code you can do :

for i,j,k,l in product(range(3),repeat=4):
    #do stuff

Based on python documentation, "This function is roughly equivalent to the following code, except that the actual implementation does not build up intermediate results in memory:"

def product(*args, repeat=1):
    # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
    # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
    pools = [tuple(pool) for pool in args] * repeat
    result = [[]]
    for pool in pools:
        result = [x+[y] for x in result for y in pool]
    for prod in result:
        yield tuple(prod)

Answered By - Mazdak