code: def delete(self, key):
          
          (_value, mem) = LRUCache.get(self, key)
          self._mem -= mem
          LRUCache.delete(self, key)
docs: >>> c = MemSizeLRUCache()
          >>> c.put(1, 1)
          >>> c.mem()
          24
          >>> c.delete(1)
          >>> c.mem()
          0