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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 severity(self, severity):
 """Sets the severity of this Message. Message severity # noqa: E501 :param severity: The severity of this Message. # noqa: E501 :type: str """

        if severity is None:
            raise ValueError("Invalid value for `severity`, must not be `None`")  # noqa: E501
        allowed_values = ["MARKETING", "INFO", "WARN", "SEVERE"]  # noqa: E501
        if severity not in allowed_values:
            raise ValueError(
                "Invalid value for `severity` ({0}), must be one of {1}"  # noqa: E501
                .format(severity, allowed_values)
            )

        self._severity = severity