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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 _value_format(self, value, serie, index):
 """ Display value and cumulation """

        sum_ = serie.points[index][1]
        if serie in self.series and (
                self.stack_from_top
                and self.series.index(serie) == self._order - 1
                or not self.stack_from_top and self.series.index(serie) == 0):
            return super(StackedLine, self)._value_format(value)
        return '%s (+%s)' % (self._y_format(sum_), self._y_format(value))