code: def _untrack_tendril(self, tendril):
          
  
          try:
              del self.tendrils[tendril._tendril_key]
          except KeyError:
              pass
  
          # Also remove from _tendrils
          try:
              del self._tendrils[tendril.proto][tendril._tendril_key]
          except KeyError:
              pass
docs: Removes the tendril from the set of tracked tendrils.