<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def paren_split(sep,string):
 """ Splits the string into pieces divided by sep, when sep is outside of parentheses. """

    if len(sep) != 1: raise Exception("Separation string must be one character long")
    retlist = []
    level = 0
    blevel = 0
    left = 0
    for i in range(len(string)):
        if string[i] == "(": level += 1
        elif string[i] == ")": level -= 1
        elif string[i] == "[": blevel += 1
        elif string[i] == "]": blevel -= 1
        elif string[i] == sep and level == 0 and blevel == 0:
            retlist.append(string[left:i])
            left = i+1
    retlist.append(string[left:])
    return retlist