how to create all possible combinations of multiple variables in python

Question

I have a arbitrary number of variables with arbitrary number of valid values each variable can take. For eg. a - (a1,a2,a3), b - (b1,b2), c - (c1,c2,c3,c4,c5). Now I wanted the a list of dictionaries as below

[
{a:a1,b:b1,c:c1},
{a:a1,b:b1,c:c2},
{a:a1,b:b1,c:c3},
.
.
.
{a:a3,b:b2,c:c3}
]

Total 3*2*5 = 30 combinations will come for the above scenario. How to create them in python.

I could have three for loops for each variable as below

result_list = list()
for a_val in [a1,a2,a3]:
    for b_val in [b1,b2]:
        for c_val in [c1,c2,c3,c4,c5]:
            result_list.append({a:a_val,b:b_val,c:c_val})

But the number of variables also vary. Instead of 3 variables, I wanted to apply on 5 variables as well (a,b,c,d,e) and so on. How to have a common code to achieve this in python

Answer 1

The simplest way to do this is itertools.product(). It allows you to create what you want in a simple one-liner:

import itertools
a = [1,2,3]
b = [4,5]
c = [-1]
# result contains all possible combinations.
combinations = list(itertools.product(a,b,c))

Note that the resulting combinations variable itself is a list(could be cast to a set), and the different elements are tuples, not dicts.

I currently don't see the exact reasoning why you would have to name your elements in a dict-like fashion, as long as you know in which order the elements are stored there (which is predictable in itertools.product.