class graphicsScene(QtGui.QGraphicsScene):

    def __init__(self, parent=None):
        super(graphicsScene, self).__init__(parent)

def mousePressEvent(self, event):
    super(graphicsScene, self).mousePressEvent(event)
item = graphicsItem()
position = QtCore.QPointF(event.scenePos()) - item.rectF.center()
item.setPos(position.x(), position.y())
self.addItem(item)
MousePressEvent, position offset in QGraphicsView