how to write the interface code

[nasr]

sorry i tried with this code also...but not working

def toggleLink():
	global link
	if link:
		#If link exits, stop grabbing
		link.remove()
		link = None

	if vizmat.Distance(hand.getPosition(), ball.getPosition()) < .5:
		link = viz.grab( hand, ball )
	if vizmat.Distance(hand.getPosition(),crank.getPosition()) < .5:
		link=viz.grab ( hand, crank)

vizact.onmousedown(viz.MOUSEBUTTON_RIGHT ,toggleLink)