Find the matching closing bracket in a long string

2026-10-22 python regex parsing · raw · python

A bracket-matching helper that ignores brackets inside quotes. The regex finds
the candidates, the scan keeps a counter, and the function returns the index
of the matching close.

import re

PAIRS = {"(": ")", "[": "]", "{": "}"}


def match_index(text: str, start: int) -> int:
    opening = text[start]
    closing = PAIRS[opening]
    depth = 0
    in_string = None
    escape = False
    for index in range(start, len(text)):
        char = text[index]
        if escape:
            escape = False
            continue
        if char == "\\":
            escape = True
            continue
        if in_string:
            if char == in_string:
                in_string = None
            continue
        if char in "\"'":
            in_string = char
            continue
        if char == opening:
            depth += 1
        elif char == closing:
            depth -= 1
            if depth == 0:
                return index
    return -1

The escape flag is what keeps a quoted backslash from ending the string early.