def does_contain(stackstrings, ss):
    """
    Check existence of stackstring in list.
    :param stackstrings: list of all recovered stackstrings
    :param ss: new stackstring candidate
    :return: True if candidate already in stackstring list, False otherwise
    """
    hashable_ss = (ss.fva, ss.s, ss.written_at)
    for s in stackstrings:
        hashable = (s.fva, s.s, s.written_at)
        if hashable == hashable_ss:
            return True
    return False