'Override Qt method'

def paintEvent(self, event):

    painter = QPainter(self)
    size = self.size()
    offsets = [(col - min(self.columns)) for col in self.columns]
    for offset in offsets:
        color = QColor(self.color)
        color.setAlphaF(0.5)
        painter.setPen(color)
        x = self.editor.fontMetrics().width((offset * '9'))
        painter.drawLine(x, 0, x, size.height())
