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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 backness(self, value):
 """ Set the backness of the vowel. :param str value: the value to be set """

        if (value is not None) and (not value in DG_V_BACKNESS):
            raise ValueError("Unrecognized value for backness: '%s'" % value)
        self.__backness = value