this would be mutation of inputs:

def in_array(a1, a2):
    a2[0] = "a"

this one: https://www.codewars.com/kata/56efc695740d30f963000557

"" - True
"[(])" - False, not completed []

I am confused as well at first.
Assuming you already know the instruction for i,d,s now let's proceed to the returning of the result.
There is no fix array length for result because array index is incrementing every 'o' So for instance:

string input = "iioio"
int result[] = {2, 3};

string input = "iodoio"
int result[] = {1, 0, 1};

I hope you understand bro!

They're out of order.

[]()
[()]
([])
()[]

Those are valid, the one you ask for, isn't.

consider the scope: within [] is an incomplete pairing: (. Similarly, the ) stands alone outside that scope as incomplete.

It's not a condition, actually, it accepts any iterable, even a generator, hence a generator comprehesion, here.

No, the arguments are not mutated.

Ternary is something like return A if B else C

This is list comprehension.

No need for expansion.

The description already said 0-9 only required.