class node:
    def __int__(self,prev=None,data=None,next=None):
        self.prev=prev
        self.data=data
        self.next=next

class doublelinkedlist:
    def __int__(self):
        self.head=None


#INSERTION BEGNING FOR DOUBLE LINKED LIST:
        def __insertion_at_begning(self,data):
            if self.head is none:
                self.head=Node(self.none,data,self.none)
                return
            self.head=Node(prev,data,self.head)
            self.head.next.prev=self.head

#FUNCTION EMPTY-LIST
            def is_empty(self):
                if self.head==None:
                    return
                self.head==None
#INSERTION AT BEGNING FOR EMPTY LIST USING DOUBLE LINKED LIST
                def __insertion_at_begning(self,data):
                    node=Node(none,data,self.head)
                    if not self is empty():
                        self.head.prev=node
                        self.head=node

#INSERTION AT END USING DOUBLE LINKED LIST:
                        def __insertion_at_end(self,data):
                            if self.head is None:
                                self.head=Node(None,data,None)
                                return
                            itr=self.head
                            while itr.next:
                                itr.next=Node(itr,data,None)