code: def get_preferred(self, addr_1, addr_2):
          '''Return the preferred address.'''
          if addr_1 > addr_2:
              addr_1, addr_2 = addr_2, addr_1
  
          return self._cache.get((addr_1, addr_2)f get_preferred(self, addr_1, addr_2):
          '''Return the preferred address.'''
          if addr_1 > addr_2:
              addr_1, addr_2 = addr_2, addr_1
  
          return self._cache.get((addr_1, addr_2))
docs: Return the preferred address.