Question

I’m trying to make a linked list class in python (pointless I know, but it’s a learning exercise), and the method I have written to remove a node doesn’t work if I try to remove the first element of the linked list. If the node to be removed is anywhere else in the linked list the method works fine. Can someone give me some insight as to where I’ve gone wrong?

Here’s my code thus far:

class Node:

    def __init__(self, data=None, next=None):
        self.data = data
        self.next = next

    def __repr__(self):
      return repr(self.data)

    def printNodes(self):
        while self:
            print self.data
            self = self.next

    def removeNode(self, datum):
        """removes node from linked list"""
        if self.data == datum:
            return self.next
        while self.next:
            if self.next.data == datum:
                self.next = self.next.next
                return self
            self = self.next

Answer 1

Modify removeNode so that it always returns the head of the linked list and then assign the result back to your head node. Like so:

def removeNode(self, datum):
    """removes node from linked list and returns head node"""
    head = self
    curr_node = self
    if curr_node.data == datum:
        head = curr_node.next
    else:
        while curr_node.next:
            if curr_node.next.data == datum:
                curr_node.next = self.next.next
                break
            curr_node = curr_node.next
    return head

Or, if you want to avoid having to assign the result of removeNode back to head:

def removeNode(self, datum):
    """removes node from linked list"""
    curr_node = self
    if curr_node.data == datum:
        # steals the the data from the second node
        curr_node.data = curr_node.next.data
        curr_node.next = curr_node.next.next
    else:
        while curr_node.next:
            if curr_node.next.data == datum:
                curr_node.next = curr_node.next.next
                break
            curr_node = curr_node.next

Note: I assigned self to curr_node because it felt wrong to modify self.