def _extract_prop_set(line):
    """
    Extract the (key, value)-tuple from a string like:
    >>> 'set foo = "bar"'
    :param line:
    :return: tuple (key, value)
    """
    token = ' = "'
    line = line[4:]
    pos = line.find(token)
    return line[:pos], line[pos + 4:-1]