linkedlist.py

class Node :
    def __init__(self, data) :
        self.data = data
        self.next = None
        
class Linkedlist :
    
    def __init__(self) :
        dummy = Node("dummy")
        self.head = dummy
        self.tail = dummy
        self.current = None
        self.before = None
        self.num_of_data = 0
        
    def append(self, data) :
        new_node = Node(data)
        self.tail.next = new_node
        self.tail = new_node
        self.tail = new_node
        self.num_of_data +=  1
        
    def delete(self) :
        pop_data = self.current.data
        
        if self.current is self.tail :
            self.tail = self.before
            
        self.before.next = self.current.next
        self.current = self.before
        
        self.num_of_data -= 1
        return pop_data
    
    def first(self) :
        if self.num_of_data == 0 :
            return None
        
        self.before = self.head
        self.current = self.head.next
        
        return self.current.data
    
   def next(self) :
    if self.current.next == None :
        return None
    
    self.before = self.current
    self.current = self.current.next
    
    return self.current.data

    def size(self) :
        return self.num_of_data