I find this little code super useful. It allows you to flop all the nodes you have selected; pretty much reverse them in X. I honestly don't know who wrote it because a coworker sent it my way when I started learning Python. I have this code set to the hotkey ctrl+alt+f.
Expand Flop Nodes
import nuke
def flopNodes():
nodes = nuke.selectedNodes()
maxX = max( [ n.xpos()+n.screenWidth()/2 for n in nodes ] )
minX = min( [ n.xpos()+n.screenWidth()/2 for n in nodes ] )
centreX = (maxX - minX)/2 + minX
for n in nodes :
n.setXpos( (centreX + (centreX - (n.xpos() + n.screenWidth()/2 )))- n.screenWidth()/2)