def is_multiline(s):
    """Returns True if the string contains more than one line.
    This tends to perform much better than len(s.splitlines()) or s.count('\n')
    :param s: string to check
    :return: Bool
    """
    start = 0
    lines = 1

    while True:
        idx = s.find('\n', start)

        if idx == -1:
            return lines > 1
        else:
            lines += 1

        if lines > 1:
            return True
        else:
            start = idx + 1