def __new__(cls, name, bases, dict_):
    """Redefines all state-altering operations to preserve sentinels
        and creates the resulting :class:`list` subclass.
        """
    assert bases == (list,)
    for op in (cls.OPERATORS + cls.METHODS):
        dict_[op] = cls.with_preserved_sentinel(op)
    return type.__new__(cls, name, bases, dict_)
