code: def _deleteTrackers(self, trackers):
          
  
          for tracker in trackers:
              if tracker.store is None:
                  # we're not updating the list of live signups client side, so
                  # we might get a signup that has already been deleted
                  continue
  
              sig = tracker.signupItem
  
              # XXX the only reason we're doing this here is that we're afraid to
              # add a whenDeleted=CASCADE to powerups because it's inefficient,
              # however, this is arguably the archetypical use of
              # whenDeleted=CASCADE.  Soon we need to figure out a real solution
              # (but I have no idea what it is). -glyph
  
              for iface in sig.store.interfacesFor(sig):
                  sig.store.powerDown(sig, iface)
              tracker.deleteFromStore()
              sig.deleteFromStore()
docs: Delete the given signup trackers and their associated signup resources.
  
          @param trackers: sequence of L{_SignupTrackers}