Python - Longest substring having only matched parentheses

For interactive parsing purposes, given an input string I need to extract the longest possible substring starting at index 0 and having only matched parentheses.

Example (LISP-like s-expressions)

Input string: (print "hello") (assign a (+ c d)) (assign e (+ f g)

Output substring: (print "hello") (assign a (+ c d))

I would like to make a simple Python function to achieve this.

Loop over the string while counting parentheses, and at the end just slice the string to the last index where the parenthesis counter was 0:

def max_parseable_substring(text):
    parentheses = 0
    end = 0

    for i, char in enumerate(text):
        if char == "(":
            parentheses += 1
        elif char == ")":
            parentheses -= 1

        if parentheses == 0:
            end = i

    return text[:end]