You will need to modify the code below with your tracker ID and machine name.
Code:
vrpn = viz.add('vrpn7.dle')
TRACKER_ID = "Trackable 1"
VRPN_MACHINE = "localhost"
headtracker = vrpn.addTracker(TRACKER_ID + "@" + VRPN_MACHINE, 0)
Replace 'Trackable 1' with the name given by the Tracking Tools software from Natural Point. Also make sure the software is streaming data.