Return a CategoryDataPoint object newly created with value *value*,
        an optional *number_format*, and appended to this sequence.

def add_data_point(self, value, number_format=None):
        """
        Return a CategoryDataPoint object newly created with value *value*,
        an optional *number_format*, and appended to this sequence.
        """
        data_point = CategoryDataPoint(self, value, number_format)
        self.append(data_point)
        return data_point