code: def paintEvent(self, event):
          
          painter = QPainter(self)
          size = self.size()
  
          color = QColor(self.color)
          color.setAlphaF(.5)
          painter.setPen(color)
  
          for column in self.columns:
              x = self.editor.fontMetrics().width(column * '9')
              painter.drawLine(x, 0, x, size.height())
docs: Override Qt method