Untitled

viewer = nuke.activeViewer()

if viewer is not None:
    for node in nuke.selectedNodes():
        node['selected'].setValue(False)
    dot = nuke.createNode("Dot", inpanel=False)
    viewer = viewer.node()
    viewer['xpos'].setValue( dot.xpos() - viewer.screenWidth()/2 )
    viewer['ypos'].setValue( dot.ypos() - viewer.screenHeight()/2)
    nuke.delete(dot)