Try using
key codes instead of numbers to get the number pad key events:
Code:
def printKey(key):
print key
vizact.onkeydown(viz.KEY_KP_0,printKey,'KP_0')
vizact.onkeydown(viz.KEY_KP_1,printKey,'KP_1')
vizact.onkeydown(viz.KEY_KP_2,printKey,'KP_2')
vizact.onkeydown(viz.KEY_KP_3,printKey,'KP_3')