code: def Put(self, key, obj):
      
      # Remove the old entry if it is there.
      node = self._hash.pop(key, None)
      if node:
        self._age.Unlink(node)
  
      # Make a new node and insert it.
      node = Node(key=key, data=obj)
      self._hash[key] = node
      self._age.AppendNode(node)
  
      self.Expire()
  
      return key
docs: Add the object to the cache.