code: def mousePressEvent(self, event):
          
          # ignore events when the scene is in view mode
          scene = self.scene()
          if scene and scene.inViewMode():
              event.ignore()
              return
  
          # block the selection signals
          if scene:
              scene.blockSelectionSignals(True)
  
              # clear the selection
              if ( not (self.isSelected() or
                                event.modifiers() == Qt.ControlModifier) ):
                  for item in scene.selectedItems():
                      if item != self:
                          item.setSelected(False)
  
          # try to start the connection
          super(XNodeConnection, self).mousePressEvent(event)
docs: Overloads the mouse press event to handle special cases and \
          bypass when the scene is in view mode.
          
          :param      event   <QMousePressEvent>