Python function to parse nested parentheses.

parse_para.py

def parse(string):
    if not string: return
    if string[0] != "(": raise ValueError("malformed string")
    parsed = ()
    last = 0
    count = 0
    for i in range(len(string)):
        if string[i] == "(": count += 1
        if string[i] == ")": count -= 1
        if count == 0:
            inner = parse(string[last+1:i])
            last = i+1
            if inner:
                parsed += (list(inner),)
            else:
                parsed += ([],)
    if last != len(string): raise ValueError("malformed string")
    return parsed