FAQ: Linked Lists: Python - Linked List Implementation I

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This community-built FAQ covers the “Linked List Implementation I” exercise from the lesson “Linked Lists: Python”.

Paths and Courses
This exercise can be found in the following Codecademy content:

Computer Science

Linear Data Structures

FAQs on the exercise Linked List Implementation I

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2

Hello,

Can somebody please explain the logic of the solution for step 1?
class LinkedList:
def init(self, value=None):
self.head_node = Node(value)

Why is it correct like this if head_node is not an argument of init()? Moreover, why is self.value = value mentioned?

My code was:
class LinkedList:
def init(self, value=None, head_node):
self.value = value
self.head_node = Node(value)

It didn’t work because I put head_node as an argument for init(). I would appreciate a clear answer so many thanks in advance!

3 Likes
3

i am facing the same question bro … have you figured it out?

4 
self.head_node = Node(value)

what is the meaning of this line?

1 Like
5

I am confused by this line of code as well…

6

As we all read before coming to this lesson, linked lists are composed of nodes. The line you guys mention self.head_node = Node(value) means that our LinkedList instance is also the head node of a linked list.

Let’s say we create an instance of the LinkedList class:

hello = LinkedList(5)

our new LinkedList instance object hello will have a self.value of 5, and will also be a head_node, which will be Node(5). Remember w/e you put into the __init__ method will happen when you create an object.

You can test putting these lines at the end of your code:

hello = LinkedList(5)
print(hello.value)
print(hello.head_node.value)
print(hello.head_node)

first and second print should return 5; the third one will tell you that it’s a .Node object. In few words: hello is LinkedList(5) and also a head_node whose value is 5, or Node(5)

4 Likes
7

Also came here seeking the answer to this question.

8

You set the self.head_node = Node(value), to be able to reach the methods of the Node class by using self.head_node

2 Likes
9

It means that, within the class LinkedList, we are setting the instance attribute (which we call head_node) equal to an instance of the class Node with data equal to “value”.

10

This question is for the page right after because I could not find the exact forum page for it (https://www.codecademy.com/courses/linear-data-structures/lessons/learn-linked-lists-python/exercises/linked-lists-python-list-ii)

Why does this while loop construction not work as intended?

def stringify_list(self):
    value_holder = ''
    node = self.get_head_node()
    while node.get_next_node() != None:
      value_holder = value_holder + '\n' + str(node.get_value())
      node = node.get_next_node()
    return value_holder
11

Linked List is explained in a difficult way in Codecademy

12

Hey guys. About this part in task 1:
We want to be able to instantiate a LinkedListwith a head node, so.init()should takevalueas an argument. Make surevaluedefaults toNone if no value is provided.

Why would the default for value in the constructor be None? I thought linked lists always have a head node, so during instantiation of the linked list, shouldn’t it have a value for the head node by necessity?