def add_ring(self, ring):
        """Adds a ring to _rings if not already existing"""
        if ring not in self._rings and isinstance(ring, RingDing0):
            self._rings.append(ring)
def add_ring ( self , ring ) : if ring not in self . _rings and isinstance ( ring , RingDing0 ) : self . _rings . append ( ring )
Adds a ring to _rings if not already existing