'Add the object to the cache.'

@Synchronized
def Put(self, key, obj):

    node = self._hash.pop(key, None)
    if node:
        self._age.Unlink(node)
    node = Node(key=key, data=obj)
    self._hash[key] = node
    self._age.AppendNode(node)
    self.Expire()
    return key
