Deleting a Head Node from Linked List in Python

Question

I have been working on linked lists in Python. I was able to create nodes, link nodes, and add new nodes, but I am really stuck at deleting the node, especially the case when the element present in the node matches with the header (first node in list) where the root pointer is pointing to it.

I have written a condition to check that the input element matches with the element in the header node and, if found, I have changed the root pointer to the next node pointer but am still not able to delete the node.

Below is the function I have created to delete the node:

import copy
class Node:
      def __init__(self,data=None):
        self.data=data
        self.pointer=None

class Llist:
      def __init__(self):
        self.rootpointer=None

      def addlist(self,newdata):
        self.newdata=newdata
        node4=Node(newdata)
        node4.pointer=self.rootpointer
        self.rootpointer=node4

      def Dispaylist(self):
        self.cpyrootpointer=copy.deepcopy(self.rootpointer)
        while self.cpyrootpointer is not None :
          print (self.cpyrootpointer.data)
          self.cpyrootpointer=self.cpyrootpointer.pointer

      def removeitem(self,item):
        self.item=item
        self.cpyrootpointerr=copy.deepcopy(self.rootpointer)
        curr=self.cpyrootpointerr
        while self.cpyrootpointerr is not None:
            if(self.cpyrootpointerr.data==item):
              self.cpyrootpointerr=curr.pointer
              break




linkedlist=Llist()
linkedlist.rootpointer=Node('A')
linkedlist.rootpointer.pointer=Node('B')
linkedlist.rootpointer.pointer.pointer=Node('C')

linkedlist.addlist('D')
linkedlist.Dispaylist()

linkedlist.addlist('E')
print('break')
linkedlist.Dispaylist()
linkedlist.removeitem('E')
linkedlist.Dispaylist()

I have E-->D--->A-->B-->C in the list. What I want is D--->A-->B-->C after I call the removeitem() function, but I am getting E-->D--->A-->B-->C again.

Answer 1

You are not changing the root pointer, you are changing a copy. "self.cpyrootpointerr=curr.pointer" should be "self.rootpointer = curr.pointer". Be aware that this only handles the case where the first item on the list is being deleted.

Answer 2

See delete function in this post

class LinkedList(Node):
    ...
    def delete(self,value):
        temp = self.__head
        while temp!=None:
            if temp.value == value and temp == self.__head:
                self.__head = temp.ref
                del temp
                self.__count -= 1
                break
            elif temp.ref != None and temp.ref.value == value:
                temp_ref = temp.ref.ref
                del temp.ref
                self.__count -= 1
                temp.ref = temp_ref
                break
            temp = temp.ref