python实现双向链表

双向链表实现append、pop、insert、remove、iternodes

class Node:
    def __init__(self, item, prev=None, next=None):
        self.item = item
        self.next = next
        self.prev = prev

    def __repr__(self):
        return '{}'.format(self.item)


class LinkedList:
    def __init__(self):
        self.head = None
        self.tail = None
        self.size = 0

    def append(self, item):
        node = Node(item)
        if self.head is None:
            self.head = node
            self.tail = node
        else:
            self.tail.next = node
            node.prev = self.tail
            self.tail = node
        return self

    def pop(self):
        if self.head is None:
            raise Exception('Empty')
        node = self.tail  # 链表的尾部
        item = node.item  # 尾部的值
        prev = node.prev
        if prev is None:  # only one
            self.head = None
            self.tail = None
        else:
            prev.next = None
            self.tail = prev
        return item

    def insert(self, index, item):
        if index < 0:
            raise IndexError
        current = None
        for i, nodes in enumerate(self.iter_nodes()):
            if i == index:
                current = nodes
                break
        else:  # 没有break，尾部追加
            self.append(item)
            return

        node = Node(item)
        prev = current.prev
        next = current
        if prev is None:
            self.head = node
            node.next = next
            next.prev = node
        else:
            prev.next = node
            next.prev = node
            node.prev = prev
            node.next = next

    def remove(self, index):
        if self.tail is None:
            raise Exception('Empty')
        if index < 0:
            raise IndexError
        current = None
        for i, nodes in enumerate(self.iter_nodes()):
            if i == index:
                current = nodes
                break
        else:
            raise IndexError
        prev = current.prev
        next = current.next

        if prev is None and next is None:
            self.head = None
            self.tail = None
        elif prev is None:  # 头部
            self.head = next
            next.prev = None
        elif next is None:  # 尾部
            self.tail = prev
            prev.next = None
        else:  # 在中间
            prev.next = next
            next.prev = prev
        del current

    def iter_nodes(self, reverse=False):
        current = self.head if not reverse else self.tail
        while current:
            yield current
            current = current.next if not reverse else current.prev