Is there a DRY way to get n Cartesian Products in Python?

Question

According to 72489951, if one wants to generate the product of a list, this function does the job.

def generate_prods():
    from itertools import product
    in_list = ['a', 'b', 'c']
    out_prods = list(product(in_list, in_list))
    return out_prods

This returns

[('a', 'a'), ('a', 'b'), ('a', 'c'), ('b', 'a'), ('b', 'b'), ('b', 'c'), ('c', 'a'), ('c', 'b'), ('c', 'c')]

This is fine unless you want to add another character. Doing so means you need to hardcode another use of the same list.

def generate_prods():
    from itertools import product
    in_list = ['a', 'b', 'c']
    out_prods = list(product(in_list, in_list, in_list))
    return out_prods

Clearly, this is not DRY, so how do you generate the Cartesian Product for length n of the same list?

score -1 · Answer 1 · answered Mar 24 '23 at 10:40

The number of times to repeat the use of the same source list can be specified using repeat;

from itertools import product


def generate_prods(source_list: list, length: int):
    out_prods = list(product(source_list, repeat=length))
    return out_prods


test_list = ['a', 'b', 'c']
for prod_length in range(5):
    print(generate_prods(source_list=test_list,
                         length=prod_length))

Output:

[()]
[('a',), ('b',), ('c',)]
[('a', 'a'), ('a', 'b'), ('a', 'c'), ('b', 'a'), ('b', 'b'), ('b', 'c'), ('c', 'a'), ('c', 'b'), ('c', 'c')]
[('a', 'a', 'a'), ('a', 'a', 'b'), ('a', 'a', 'c'), ('a', 'b', 'a'), ('a', 'b', 'b'), ('a', 'b', 'c'), ('a', 'c', 'a'), ('a', 'c', 'b'), ('a', 'c', 'c'), ('b', 'a', 'a'), ('b', 'a', 'b'), ('b', 'a', 'c'), ('b', 'b', 'a'), ('b', 'b', 'b'), ('b', 'b', 'c'), ('b', 'c', 'a'), ('b', 'c', 'b'), ('b', 'c', 'c'), ('c', 'a', 'a'), ('c', 'a', 'b'), ('c', 'a', 'c'), ('c', 'b', 'a'), ('c', 'b', 'b'), ('c', 'b', 'c'), ('c', 'c', 'a'), ('c', 'c', 'b'), ('c', 'c', 'c')]
[('a', 'a', 'a', 'a'), ('a', 'a', 'a', 'b'), ('a', 'a', 'a', 'c'), ('a', 'a', 'b', 'a'), ('a', 'a', 'b', 'b'), ('a', 'a', 'b', 'c'), ('a', 'a', 'c', 'a'), ('a', 'a', 'c', 'b'), ('a', 'a', 'c', 'c'), ('a', 'b', 'a', 'a'), ('a', 'b', 'a', 'b'), ('a', 'b', 'a', 'c'), ('a', 'b', 'b', 'a'), ('a', 'b', 'b', 'b'), ('a', 'b', 'b', 'c'), ('a', 'b', 'c', 'a'), ('a', 'b', 'c', 'b'), ('a', 'b', 'c', 'c'), ('a', 'c', 'a', 'a'), ('a', 'c', 'a', 'b'), ('a', 'c', 'a', 'c'), ('a', 'c', 'b', 'a'), ('a', 'c', 'b', 'b'), ('a', 'c', 'b', 'c'), ('a', 'c', 'c', 'a'), ('a', 'c', 'c', 'b'), ('a', 'c', 'c', 'c'), ('b', 'a', 'a', 'a'), ('b', 'a', 'a', 'b'), ('b', 'a', 'a', 'c'), ('b', 'a', 'b', 'a'), ('b', 'a', 'b', 'b'), ('b', 'a', 'b', 'c'), ('b', 'a', 'c', 'a'), ('b', 'a', 'c', 'b'), ('b', 'a', 'c', 'c'), ('b', 'b', 'a', 'a'), ('b', 'b', 'a', 'b'), ('b', 'b', 'a', 'c'), ('b', 'b', 'b', 'a'), ('b', 'b', 'b', 'b'), ('b', 'b', 'b', 'c'), ('b', 'b', 'c', 'a'), ('b', 'b', 'c', 'b'), ('b', 'b', 'c', 'c'), ('b', 'c', 'a', 'a'), ('b', 'c', 'a', 'b'), ('b', 'c', 'a', 'c'), ('b', 'c', 'b', 'a'), ('b', 'c', 'b', 'b'), ('b', 'c', 'b', 'c'), ('b', 'c', 'c', 'a'), ('b', 'c', 'c', 'b'), ('b', 'c', 'c', 'c'), ('c', 'a', 'a', 'a'), ('c', 'a', 'a', 'b'), ('c', 'a', 'a', 'c'), ('c', 'a', 'b', 'a'), ('c', 'a', 'b', 'b'), ('c', 'a', 'b', 'c'), ('c', 'a', 'c', 'a'), ('c', 'a', 'c', 'b'), ('c', 'a', 'c', 'c'), ('c', 'b', 'a', 'a'), ('c', 'b', 'a', 'b'), ('c', 'b', 'a', 'c'), ('c', 'b', 'b', 'a'), ('c', 'b', 'b', 'b'), ('c', 'b', 'b', 'c'), ('c', 'b', 'c', 'a'), ('c', 'b', 'c', 'b'), ('c', 'b', 'c', 'c'), ('c', 'c', 'a', 'a'), ('c', 'c', 'a', 'b'), ('c', 'c', 'a', 'c'), ('c', 'c', 'b', 'a'), ('c', 'c', 'b', 'b'), ('c', 'c', 'b', 'c'), ('c', 'c', 'c', 'a'), ('c', 'c', 'c', 'b'), ('c', 'c', 'c', 'c')]

FWIW, the function `generate_prods` really doesn't add a lot here. Just `print(list(product(test_list, repeat=prod_length)))` reads pretty much the same… — deceze, Mar 24 '23 at 10:44
True, however, this is just to demonstrate. In another application, one might want to do some stuff before `return` — James Geddes, Mar 24 '23 at 10:46
Since you're just demonstrating the `repeat` parameter of `product`, such hypothetical other implementations are fairly irrelevant… — deceze, Mar 24 '23 at 10:48

Is there a DRY way to get n Cartesian Products in Python?

1 Answers1