Why do I have an error saying that "self" is not defined?

I am creating a linked list where I insert at the beginning of the list but i keep on getting that "NewNode" in NewNode.nextval = self.headval and "self" in self.headval = NewNode is undefined

Here is my code:

# creation of linked list
class Node:
    def __init_(self, dataval=None):
        self.dataval = dataval
        self.nextval = None
        
class linked_list:
    def __init__(self):
        self.headval = None
# Print linked list        
    def listprint(self):
        printval = self.headval
        while printval is not None:
            print(printval.dataval)
            printval = printval.nextval
    def AtStart(self,newdata):
       NewNode = Node(newdata)
# for updating new nodes next val to existing node
    
    NewNode.nextval = self.headval
    self.headval = NewNode
    
list = linked_list()
list.headval = Node("2")
e2 = Node("3")
e3 = Node("4")
list.headval.nextval = e2
e2.nextval = e3
list.AtStart("1")
list.listprint()

>Solution :

Well you have a few problems.

1. You are missing an underscore in the init method of Node change it to def __init__
2. There are a few lines which probably should be part of AtStart but aren’t because of indentation

Change

def AtStart(self,newdata):
   NewNode = Node(newdata)
# for updating new nodes next val to existing node
    
NewNode.nextval = self.headval
self.headval = NewNode

to

def AtStart(self, newdata):
    NewNode = Node(newdata)

    # for updating new nodes next val to existing node
    NewNode.nextval = self.headval
    self.headval = NewNode