Returns the minimum label width required on this renderers font size.
        
        :param      labels | [<str>, ..]

def minimumLabelWidth(self):
        """
        Returns the minimum label width required on this renderers font size.
        
        :param      labels | [<str>, ..]
        """
        min_w = 0
        metrics = QFontMetrics(self.labelFont())
        for label in self.labels():
            min_w = max(min_w, metrics.width(label))
        
        return max(self._minimumLabelWidth,
                   min_w + self.horizontalLabelPadding())