# 队列两端都可以进行push和pop操作。 push操作可以用循环双端链表的append，appendleft。
# pop操作使用循环双端链表的romoveclass Node(object): # 结点有两个指针def __init__(self, maxsize = None, value = None, next = None, prev = None):self.maxsize = maxsizeself.value = valueself.next = nextself.prev = prevclass Dqueue(object):def __init__(self, maxsize = None):self.maxsize = maxsizenode = Node()node.next = nodenode.prev = node # 最开始的只有根结点，它自己两个指针指向自己self.root = nodeself.length = 0def __len__(self):return self.lengthdef headnode(self):return self.root.nextdef tailnode(self):return self.root.prevdef push(self, value):    # 在右端压入值，相当于循环双端链表的appendif self.maxsize is not None and len(self) >= self.maxsize:raise Exception('full')node = Node(value = value)tailnode = self.tailnode() # 获取尾结点， 这个这次append 是插入的第一个结点。 尾结点就是self.root (根结点)tailnode.next = nodenode.prev = tailnodenode.next = self.rootself.root.prev = nodeself.length += 1def pushleft(self, value):if self.maxsize is not None and len(self) >= self.maxsize:raise Exception('full')node = Node(value = value)if self.root.next == self.root:  # 最初只有一个根结点的情况self.root.next = nodeself.root.prev = nodenode.next = self.rootnode.prev = self.rootelse:head = self.root.nextnode.next = headnode.prev = self.rootself.root.next = nodehead.prev = nodeself.length += 1def remove(self, node):       # 注意这里传入的是一个node， 不是传入一个值。 为了，降低算法复杂度if node is self.root:return "不能移除根结点"node.prev.next = node.nextnode.next.prev = node.prevself.length -= 1del nodedef iter_node(self):     #  遍历结点if self.root.next == self.root: # 只有根结点return "队列为空"curnode = self.root.nextwhile curnode.next is not self.root:yield curnodecurnode = curnode.nextyield curnode    # 尾结点也要遍历def __iter__(self):for node in self.iter_node():yield node.valuedef iter_node_reverse(self): # 反向遍历if self.root.prev is self.root:returncurnode = self.root.prev    # tailnodewhile curnode.prev is not self.root:yield curnodecurnode =  curnode.prevyield curnodedef pop(self):tailnode = self.tailnode()self.remove(tailnode)def popleft(self):head = self.headnode()self.remove(head)def test_Dqueue():  # 测试函数 就测试了主要的pop和pushdq = Dqueue()dq.push(1)dq.push(2)assert len(dq) == 2assert list(dq) == [1,2]dq.pushleft(3)assert list(dq) == [3,1,2]dq.pop()assert list(dq) == [3,1]dq.popleft()assert list(dq) == [1]