Update

Author: Sonawane-Karan26

Chapter04/doubly_linked_list.py

@@ -4,7 +4,7 @@ def __init__ (self, data = None, next = None, prev = None):
         self.next = next
         self.prev = prev
 
-class DoublyLinkedList(object):
+class DoublyLinkedList:
     def __init__ (self):
         self.head = None
         self.tail = None
@@ -49,21 +49,68 @@ def append_at_a_location(self, data):
             prev = current
             current = current.next            
 
+    def iter(self):
+        current = self.head 
+        while current:
+            val = current.data 
+            current = current.next 
+            yield val
+            
+
+    def contains(self, data):  
+        for node_data in self.iter():  
+            if data == node_data:  
+                print(" Data item is present in the list. ") 
+                return    
+        print(" Data item is not present in the list. ") 
+        return   
+
+
 
 
 words = DoublyLinkedList()
 words.append('egg')
 words.append('ham')
 words.append('spam')
 
+print("Items in doubly linked list before append")
 current = words.head
 while current:
     print(current.data)
     current = current.next
 
+words.append_at_start('book')
+
+print("Items in doubly linked list after append")
+current = words.head
+while current:
+    print(current.data)
+    current = current.next
+
+
+words.append('book')
+
+print("Items in doubly linked list after adding element at end.")
+current = words.head
+while current:
+    print(current.data)
+    current = current.next
 
+
+
 words.append_at_a_location('ham')
+print("Doubly linked list after adding an element after word \"ham\" in the list.")
 current = words.head
 while current:
     print(current.data)
     current = current.next
+
+
+words = DoublyLinkedList()  
+words.append('egg')  
+words.append('ham')  
+words.append('spam') 
+
+
+words.contains("ham")  
+words.contains("ham2")