Trying to insert and print the data in linked list, got an error 'int' object has no attribute 'data'

Question

1. creating a linked list
2. inserting new data in linked list at end
3. printing linked list in list

Expected output: [5,6,2,8]

    class node():
        def __init__(self, data):
            self.data = data
            self.next = None
    class linkedlist():
        def add_at_end(self,newval,head):
            newnode = node(newval)
            while head.next:
                head = head.next
            head.next = newval
        def print_list(self,head):    
            LL = []
            while head:
                LL.append(head.data)
                head = head.next
            return LL
    

    x = node(5)
    y = node(6)
    z = node(2)
    
    x.next = y
    y.next = z
    vals = linkedlist()
    print(vals.add_at_end(8,x))
    print(vals.print_list(x))

Answer 1

The error occurs because you have head.next = newval where newval is a number, but you should be assigning a node instance, i.e. newnode. So the next time you iterate the list, like in print_list you'll bump into that integer, and access its data attribute, as if it is a node...

Some other remarks on your code:

• Your linkedlist class has no state. It merely provides some functions that act on the head argument. The OOP way to do this, is to give a linkedlist instance its own head attribute. And then rely on the self argument, which in your current code is not used in the functions.

• Your main code should not have to deal with node instances. It should just have to create a linkedlist, and then populate it by calling its method(s). For that to work you'll have to deal with the case where the list is empty, and a first value is added to it, because then its head attribute needs to be set to it.

• Use PascalCase for naming your classes.

• The name of the print_list function is misleading: it doesn't print, but returns a list. So I would name it to_list instead.

• Don't print the result of calling vals.add_at_end, because it is not designed to return anything, so you'll be printing None.

Corrected:

class Node():  # Use PascalCase
    def __init__(self, data):
        self.data = data
        self.next = None


class LinkedList():
    def __init__(self):
        self.head = None  # Give each instance its own head attribute

    def add_at_end(self, newval):
        if not self.head:  # Deal with this case
            self.head = Node(newval)
        else:
            head = self.head  # Use attribute
            while head.next:
                head = head.next
            head.next = Node(newval)  # corrected  

    def to_list(self):  # Better name
        LL = []
        head = self.head  # Use attribute
        while head:
            LL.append(head.data)
            head = head.next
        return LL


vals = LinkedList()
vals.add_at_end(5)  # Use method to add nodes
vals.add_at_end(6)
vals.add_at_end(2)
vals.add_at_end(8)  # Nothing to print here
print(vals.to_list())