util.py 文件源码

def __new__(cls, arg):
        values = set([
                    c for c
                    in re.split('\s*,\s*', arg or "")
                    if c
                ])

        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