util.py 文件源码

def __new__(cls, value_list):
        if isinstance(value_list, util.string_types) or value_list is None:
            return cls.from_string(value_list)
        values = set(value_list)
        if values.difference(cls._allowed_cascades):
            raise sa_exc.ArgumentError(
                "Invalid cascade option(s): %s" %
                ", ".join([repr(x) for x in
                           sorted(values.difference(cls._allowed_cascades))]))

        if "all" in values:
            values.update(cls._add_w_all_cascades)
        if "none" in values:
            values.clear()
        values.discard('all')

        self = frozenset.__new__(CascadeOptions, values)
        self.save_update = 'save-update' in values
        self.delete = 'delete' in values
        self.refresh_expire = 'refresh-expire' in values
        self.merge = 'merge' in values
        self.expunge = 'expunge' in values
        self.delete_orphan = "delete-orphan" in values

        if self.delete_orphan and not self.delete:
            util.warn("The 'delete-orphan' cascade "
                      "option requires 'delete'.")
        return self