docs: def showEvent(self, event):
          """
          Displays this dialog, centering on its parent.
  
          :param      event | <QtCore.QShowEvent>
          """
          super(QDialog, self).showEvent(event)
  
          if not self._centered:
              self._centered = True
              try:
                  window = self.parent().window()
                  center = window.geometry().center()
              except AttributeError:
                  return
              else:
                  self.move(center.x() - self.width() / 2, center.y() - self.height() / 2)