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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def scope(self, scope):
 """Sets the scope of this Message. The audience scope that this message should reach # noqa: E501 :param scope: The scope of this Message. # noqa: E501 :type: str """

        if scope is None:
            raise ValueError("Invalid value for `scope`, must not be `None`")  # noqa: E501
        allowed_values = ["CLUSTER", "CUSTOMER", "USER"]  # noqa: E501
        if scope not in allowed_values:
            raise ValueError(
                "Invalid value for `scope` ({0}), must be one of {1}"  # noqa: E501
                .format(scope, allowed_values)
            )

        self._scope = scope