class Registry(dict):

    unregister = dict.__delitem__

    def check_key(self, key):
        pass

    def check_value(self, value):
        pass

    def check(self, key, value):
        try:
            self.check_key(key)
        except KeyError:
            raise
        except Exception as e:
            raise KeyError(e.message)

        try:
            self.check_value(value)
        except ValueError:
            raise
        except Exception as e:
            raise ValueError(e.message)

    def register(self, key, value):
        self.__setitem__(key, value)

    def __setitem__(self, key, value):
        self.check(key, value)
        super().__setitem__(key, value)