| 123456789101112131415161718192021222324 | from .model import modelclass single_set_model(model):    content = NotImplemented    def _single_validator(self) -> callable:        raise NotImplementedError()    def _validators(self) -> dict:        return {            "content": self._single_validator()        }    def __new__(cls, *args, **kwargs) -> object:        if cls.content == NotImplemented:            raise NotImplementedError("Attribute content must be field.")        super().__new__(*args, **kwargs)    def __repr__(self) -> str:        return type(self).__name__ + ": \"" + str(self) + "\""    def __str__(self) -> str:        return self.content
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