Recursion and permutations: print all permutations filling a list of length N

[SantiagoPB]

Hello everyone ,

I have written a code using recursion, which follows the following rules:

RULES
2 inputs:

• 1st input: define the length of the output, as an integer.
  

• 2nd input: write all elements that user want, as a string, that will be part of the output.
  

With these two inputs, the program must do the following:

• 1st. Find all possible substrings of the length entered in the input, [] * 1st input.
  

• 2nd. Form all the possible combinations with the elements entered in the 2nd input.
  

• 3rd. Print all possible combinations of length [] * 1st input, with the elements of the 2nd input, without repeating.
  

CODE
My code is as follows and it fails to give the length of the output:

def stringPermutations(string, prefix, permutation_list):
    if len(string) == 0:
        permutation_list.append(prefix)
    else:
        for i in range(len(string)):
            rem = string[0:i] + string[i + 1:]
            stringPermutations(rem, prefix + string[i], permutation_list)
    return sorted(list(dict.fromkeys(permutation_list)))
def main():
    n = int(input("write size: "))
    b = str(input("Write String: "))
    permutation_list = [] * n
    print(stringPermutations(b, " ", permutation_list))

if __name__ == '__main__':
    main()

EXAMPLE OF HOW SHOULD WORK:
Input: 2
+x#
Output:
+ x
+ #
x +
x #
# +
# x

Could someone tell me why it doesn't work?
Thank you very much for the help!