def insert(self, node, value):
'insert valut after node specified'
t = Node(value)
n = node.next
if n is not None:
t.next = n
n.pre = t
node.next = t
t.pre = node
return node
def append(self, value):
if self.__first is None and self.__last is None:
self._first = Node(value)
self.__last = self.__first
elif self.__first == self.__last:
n = Node(value)
self.__last = n
self.__last.pre = self.__first
self.__first.next = self.__last
else:
n = Node(value)
self.__last.next = n
n.pre = self.__last
self.__last = n
