parsing nested parentheses in python, grab content by level

Question

Apparently this problem comes up fairly often, after reading

Regular expression to detect semi-colon terminated C++ for & while loops

and thinking about

Answer 1

#!/usr/bin/env python
import re

def ParseNestedParen(string, level):
    """
    Generate strings contained in nested (), indexing i = level
    """
    if len(re.findall("\(", string)) == len(re.findall("\)", string)):
        LeftRightIndex = [x for x in zip(
        [Left.start()+1 for Left in re.finditer('\(', string)], 
        reversed([Right.start() for Right in re.finditer('\)', string)]))]

    elif len(re.findall("\(", string)) > len(re.findall("\)", string)):
        return ParseNestedParen(string + ')', level)

    elif len(re.findall("\(", string)) < len(re.findall("\)", string)):
        return ParseNestedParen('(' + string, level)

    else:
        return 'fail'

    return [string[LeftRightIndex[level][0]:LeftRightIndex[level][1]]]

Tests:

if __name__ == '__main__':

    teststring = "outer(first(second(third)second)first)outer"

    print(ParseNestedParen(teststring, 0))
    print(ParseNestedParen(teststring, 1))
    print(ParseNestedParen(teststring, 2))

    teststring_2 = "outer(first(second(third)second)"

    print(ParseNestedParen(teststring_2, 0))
    print(ParseNestedParen(teststring_2, 1))
    print(ParseNestedParen(teststring_2, 2))

    teststring_3 = "second(third)second)first)outer"

    print(ParseNestedParen(teststring_3, 0))
    print(ParseNestedParen(teststring_3, 1))
    print(ParseNestedParen(teststring_3, 2))

output:

Running tool: python3.1

['first(second(third)second)first']
['second(third)second']
['third']
['first(second(third)second)']
['second(third)second']
['third']
['(second(third)second)first']
['second(third)second']
['third']
>>>