Returns the minimum height that will be required based on this font size
        and labels list.

def minimumLabelHeight(self):
        """
        Returns the minimum height that will be required based on this font size
        and labels list.
        """
        metrics = QFontMetrics(self.labelFont())
        return max(self._minimumLabelHeight,
                   metrics.height() + self.verticalLabelPadding())