Parse json from piece of html/script

parse_json_from_string.py

def _get_json_from_string(s):
    """Parses first found json object from string (piece of html).

    >>> _get_json_from_string('{"a": "b"}')
    {u'a': u'b'}
    >>> _get_json_from_string('dskljasd{"a": "b"}asdkljasd')
    {u'a': u'b'}
    >>> _get_json_from_string('require(asd=[{"a": "b"}, {"c":"d"}]spamspamspam)')
    [{u'a': u'b'}, {u'c': u'd'}]
    >>> _get_json_from_string('{"a": [1,2,{"b":"d[1,2,3]sd"}]}')
    {u'a': [1, 2, {u'b': u'd[1,2,3]sd'}]}
    >>> _get_json_from_string('xxxxxx')
    >>> _get_json_from_string('{{}')
    Traceback (most recent call last):
        ...
    RuntimeError: Incorrect json format: not all brances closed
    >>> _get_json_from_string('{]{}')
    Traceback (most recent call last):
        ...
    RuntimeError: Incorrect json format
    """

    stack = []

    start_idx = 0
    while start_idx < len(s) and not s[start_idx] in {'{', '['}:
        start_idx += 1

    if start_idx == len(s):
        return None

    end_idx = start_idx

    open_close_map = {
        '{': '}',
        '[': ']',
    }

    in_quotes = False
    slashed_next = False

    for c in s[start_idx:]:
        end_idx += 1

        if in_quotes:

            if c == '"' and not slashed_next:
                in_quotes = False
                slashed_next = False
            if c == '\\' and not slashed_next:
                slashed_next = True
            else:
                slashed_next = False

        elif c == '"':
            in_quotes = True

        elif c in {'[', '{'}:
            stack.append(c)

        elif c in {']', '}'}:
            opener = stack.pop()
            if open_close_map[opener] != c:
                raise RuntimeError('Incorrect json format')

        if not stack:
            break

    if stack:
        raise RuntimeError('Incorrect json format: not all brances closed')

    return json.loads(s[start_idx:end_idx])