You're asking whether it is more "accurate and secure" to have a Node constructor that does not take a next argument, and give the following in defence:
it should be the role and responsibility of the Linked List Class to modify the Node’s “Next” property
This is a true statement, but whether or not the Node constructor has this extra parameter does not really have an impact on that. The LinkedList class will need a way to link nodes together, which means that the Node class has to expose a way to do that, either via a method, or by directly setting its next attribute, or ... via the constructor. For instance, if the LinkedList has a method to insert a value at a given index, then two Node-referencing attributes will need to be set: the new node's next attribute and the next attribute of the new node's predecessor (or the head reference of the linked list).
making the code more secure and removing the possibility of accidental modification.
The LinkedList class should of course be designed so that there is no room for accidents. The risk is more at the side of the code that will use the LinkedList class.
The two implementations you have provided can hardly be compared, as the second one doesn't even offer methods to manipulate the linked list -- it doesn't have code that creates/adds nodes to its list. Apparently the user of these classes is supposed to create the Node instances themselves, which really is a bad idea. The first one implements a doubly linked list, and also maintains a reference to the tail node. As it provides methods for managing the linked list, it is superior to the second implementation. On the negative side, the first implementation has methods that return Node instances to the caller, who could then (accidentally?) set the next attribute of this node potentially breaking the linked list.
To better protect the linked list from "accidents", you could decide to not expose any Node reference to the code that instantiates a LinkedList. This you don't achieve by removing the next parameter fro the Node constructor, but by forbidding (or at least discouraging) the user of your LinkedList class to tamper with the nodes that are in the list. You can achieve that by taking the following measures:
- Make clear that the head reference (and tail reference, if there is one) is an internal implementation detail. In Python you do this by naming it with an underscore (
_head).
- Don't have methods in the
LinkedList class that take a Node reference as argument, nor that return or yield a Node reference.
This way the user of LinkedList will never access the nodes directly, but will only communicate values with the LinkedList class.
Having the next parameter in the Node constructor can actually help to make the LinkedList implementation more concise.
Here is a possible implementation of such "protective" LinkedList class:
class LinkedList:
class Node:
def __init__(self, value, next=None):
self.value = value
self.next = next
def get(self, index):
if index >= 0:
for _ in range(index):
self = self.next
if not self:
break
return self
def __init__(self, *values):
self._head = None
for value in reversed(values):
self.push(value)
def isempty(self):
return not self._head
def push(self, value):
self._head = self.Node(value, self._head)
def pop(self):
if not self.isempty():
value = self._head.value
self._head = self._head.next
return value
def insert(self, index, value):
if index == 0:
return self.push(value)
prev = self._head.get(index - 1)
if prev:
prev.next = self.Node(value, prev.next)
def delete(self, index):
if index == 0:
return self.pop()
prev = self._head.get(index - 1)
if prev and prev.next:
value = prev.next.value
prev.next = prev.next.next
return value
def __iter__(self):
node = self._head
while node:
yield node.value # don't expose nodes; only values
node = node.next
lst = LinkedList(10, 20, 30, 40)
print(lst.pop()) # 10
print(*lst) # 20 30 40
lst.insert(1, 10)
print(*lst) # 20 10 30 40
lst.insert(4, 50)
print(*lst) # 20 10 30 40 50
lst.delete(4)
print(*lst) # 20 10 30 40
lst.delete(0)
print(*lst) # 10 30 40