class Node(object):
    def __init__(self,val,p=0):
        self.data = val
        self.next = p
        self.prev = p

class LinkList(object):
    def __init__(self):
        self.head = 0

    def __getitem__(self, key):

        if self.is_empty():
            print 'linklist is empty.'
            return

        elif key self.getlength():
            print 'the given key is error'
            return

        else:
            return self.getitem(key)

    def __setitem__(self, key, value):

        if self.is_empty():
            print 'linklist is empty.'
            return

        elif key self.getlength():
            print 'the given key is error'
            return

        else:
            self.delete(key)
            return self.insert(key)

    def initlist(self,data):

        self.head = Node(data[0])

        p = self.head

        for i in data[1:]:
            node = Node(i)
            p.next = node
            node.prev  = p
            p = p.next

    def getlength(self):

        p =  self.head
        length = 0
        while p!=0:
            length+=1
            p = p.next

        return length

    def is_empty(self):

        if self.getlength() ==0:
            return True
        else:
            return False

    def clear(self):

        self.head = 0

    def append(self,item):

        q = Node(item)
        if self.head ==0:
            self.head = q
        else:
            p = self.head
            while p.next!=0:
                p = p.next
            p.next = q
            q.prev = p

    def getitem(self,index):

        if self.is_empty():
            print 'Linklist is empty.'
            return
        j = 0
        p = self.head

        while p.next!=0 and j