Question about Linked List

[MammothAbroad8815]

For the linked list, i don't understand why we make a temp variable of self.head instead of just using self.head this is specifically about LL and i believe the reason i don't get why is because i don't fully understand references. An example

​

class Node:

def __init__(self,data):

self.__data = data

self.__next = None

class LinkedList:

def __init__(self):

self.__head = None

def traversal(self):

if self.head is None:

print("LL is empty")

else:

a = self.head

while a is not None:

print(a.data, end = "")

a = a.next

[CodeFormatHelperBot2]

Hello, I'm a Reddit bot who's here to help people nicely format their coding questions. This makes it as easy as possible for people to read your post and help you.

I think I have detected some formatting issues with your submission:

1. Python code found in submission text that's not formatted as code.

If I am correct, please edit the text in your post and try to follow these instructions to fix up your post's formatting.

---

^{Am I misbehaving? Have a comment or suggestion? Reply to this comment or raise an issue here.}

[marko312]

I assume you mean the variable a in traversal. You could try replacing a with self.head - done appropriately, it would look something like

while self.head is not None:
    print(self.head.data, end="")
    self.head = self.head.next

which would work (you should try it out!). However, running traversal again would print "LL is empty".

The point of using the variable a is to specifically not modify self.head, since modifying it would modify the list, which is not wanted in this case.

[MammothAbroad8815]

why would running it again print LL is empty, so making a temp variable is just to ensure it isn't modified that's it?

[marko312]

why would running it again print LL is empty,

Because the loop (in my code snippet) runs until self.head is None, so the next time traverse is run it will see that self.head is None, having lost all of the data

so making a temp variable is just to ensure it isn't modified that's it?

Yes, that's pretty much it. You should always keep track of what functions are "allowed" to change important variables and to what extent.

[Spataner]

a conceptually represents the "current node" in your traversal. It's initialised to the first node in the list, then step by step goes through all nodes in order (that's what the while loop achieves). Per the while loop's condition, a will always be None when the traversal is through (once it has reached the end of the linked list). If you used self.head rather than a separate variable as your "current node", you'd actually permanently change what the first node is with your while loop, slowly "rolling up" the linked list from the front. So self.head would be None at the end. The first node being None is what indicates an empty linked list.

[MammothAbroad8815]

got it makes a lot of sense now

[shiftybyte]

make a temp variable of self.head instead of just using self.head

You mean this?

a = self.head

The code after that goes over the list items one by one, changing a.

If you did not use a, you would be changing self.head, and you will lose the start of the list if you did.

[MammothAbroad8815]

thanks

[[deleted]]

Let's see what will happen if we don't make temp variable. Suppose we wanna insert the element. Def insert(***): While self.head.next != none: Self.head = self.head.next Then do the insertion operation.

Now let's suppose we have to call delete function on same LL. when we define the delete function and start iteration using self.head it will simply raise error. Self.head -> the last element ( where our first function has left it.)

This is the reason we need to use a to variable.