Different results from Python shell and CheckiO

I would like to give some feedback about ...

From: https://py.checkio.org/mission/brackets/solve/

HTTP_USER_AGENT:

Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.99 Safari/537.36

open_brackets="([{"
close_brackets=")]}"
open_bracket=[]
close_bracket=[]

def checkio(expression):
    for b in expression:
        if b in open_brackets:
            position_open=open_brackets.index(b)
            open_bracket.append(position_open)
            print(b)
            print (open_bracket)
        if b in close_brackets:
            position_close=close_brackets.index(b)
            close_bracket.append(position_close)
            print(b)
            print (close_bracket)
    if open_bracket==close_bracket[::-1]:
        return True
    else:
        return False

#print(checkio("{[(3+1)+2]+}"))

In my Python shell when I print the result is True but in CheckiO the result is False. I've went through the whole thing several times and have no clue.