unhashable type: 'list' when creating a combination function with Python

I’m currently trying to create a combination function that has the equal function to the itertools.combinations.

The following code is the code that I am working on:

def my_combs(s, num):
    if num == 0:
        return [[]]
    res = []
    for i in range(0, len(s)):
        m = s[i]
        rems = s[i + 1:]
        for p in my_combs(rems, num-1):
            res.append([m]+p)
    return res

from itertools import combinations
test = [1, 2, 3, 4]
print(set(combinations(test, 2)))
print(set(my_combs(test, 2)))

The result I want to get is

{(1, 2), (1, 3), (1, 4), (2, 3), (3, 4), (2, 4)}

But I keep getting an error that says unhashable type: 'list'

And then, when I change the print(set(my_combs(test, 2))) to print(my_combs(test, 2)), I get

[[1, 2], [1, 3], [1, 4], [2, 3], [2, 4], [3, 4]] 

While the elements of the results seem to be the same,

I want to get the results in tuples (i.e { ( ) } ), instead of lists (i.e [ [ ] ]).

Is there any way for me to solve the error and get the results I want with the condition of unchanging any of the print statements?

(i.e I want to have the print statement as print(set(my_combs(test, 2))) and change only the my_combs() function)

>Solution :

If you want tuples instead of lists – just use tuples instead of lists 🙂

def my_combinations(s, num):
    if num == 0:
        return [()]                              # HERE
    res = []
    for i in range(0, len(s)):
        m = s[i]
        rems = s[i + 1:]
        for p in my_combinations(rems, num-1):
            res.append((m,)+p)                   # HERE
    return res

from itertools import combinations
test = [1, 2, 3, 4]
print(set(combinations(test, 2)))
print(set(my_combinations(test, 2)))

Note that one-element tuple has to have a comma in it: (m,); without it, (m), it is just something in parentheses.