the doubly linked list is a list in which each node has three parts. one info part and two links part. one link part refers to the net node and other link nodes refer to the previous node.

as you see in the doubly linked list first node's previous link part is always none and the last node's next link is always none. it can be traversed in both forward and backward directions.
Implementation of some operations is easier, like insertion, deletion can be done with only a single reference.

Extra space is required for storing the previous link.
while inserting and deleting some extra steps are required for maintaining the previous link.

#### Doubly linked list program using python programming.

```class Node(object):

def __init__(self, value):
self.info = value
self.prev = None        self.next = None

def __init__(self):
self.start = None
def display_list(self):
if self.start is None:
print("LIst is empty")
return
print("List is : ")
p = self.start
while p is not None:
print(p.info, " ", end='')
p = p.next
print()

def insert_in_beginning(self, data):
temp = None(data)
temp.next = self.start
self.start.prev = temp
self.start = temp

def insert_in_empty_list(self, data):
temp = Node(data)
self.start = temp

def insert_at_end(self, data):
temp = Node(data)
p = self.start
while p.next is not None:
p = p.next
p.next = temp
temp.prev = p

def create_list(self):
n = int(input("Enter the number of nodes : "))
if n == 0:
return        data = int(input("Enter the first element to be inserted : "))
self.insert_in_empty_list(data)

for i in range(n - 1):
data = int(input("Enter the next element to be inserted : "))
self.insert_at_end(data)

def insert_after(self, data, x):
temp = Node(data)
p = self.start
while p is not None:
if p.info == x:
break            p = p.next

if p is None:
print(x, " not present in the list")
else:
temp.prev = p
temp.next = p.next
if p.next is not None:
p.next.prev = temp
p.next = temp

def insert_before(self, data, x):
if self.start is None:
print("List is empty")
return
if self.start.info == x:
temp = Node(data)
temp.next = self.start
self.start.prev = temp
self.start = temp
return
p = self.start
while p is not None:
if p.info == x:
break            p = p.next

if p is None:
print(x, " not present in the list")
else:
temp = Node(data)
temp.prev = p.prev
temp.next = p
p.prev.next = temp
p.prev = temp

def delete_first_node(self):
if self.start is None:
return        if self.start.next is None:
self.start = None            return        self.start = self.start.next
self.start.prev = None
def delete_last_node(self):
if self.start is None:
return        if self.start.next is None:
self.start = None            return
p = self.start
while p.next != None:
p = p.next
p.prev.next = None
def delete_node(self, x):
if self.start is None:
return        if self.start.next is None:
if self.start.info == x:
self.start = None            else:
return
if self.start.info == x:
self.start = self.start.next
self.start.prev = None            return
p = self.start.next
while p.next is not None:
if p.info == x:
break
p = p.next

if p.next is not None:
p.prev.next = p.next
p.next.prev = p.prev
else:
if p.info == x:
p.prev.next
else:

def reverse_list(self):
if self.start is None:
return
p1 = self.start
p2 = p1.next
p1.next = None        p1.prev = p2
while p2 is not None:
p2.prev = p2.next
p2.next = p1
p1 = p2
p2 = p2.prev
self.start = p1

#################################################################3

list.create_list()

while True:
print("1. Display list")
print("2. Insert in empty list")
print("3. Insert a node in the beginning of the list")
print("4. Insert a node at the end of the list")
print("5. Insert a node after a specified node")
print("6. Insert a node before a specified node")
print("7. Delete first node")
print("8. Delete last node")
print("9. Delete any node")
print("10. Reverse the list")
print("11. Quit")

option = int(input("Enter your choice : "))

if option == 1:
list.display_list()
elif option == 2:
data = int(input("Enter the element to be inserted : "))
list.insert_in_empty_list(data)
elif option == 3:
data = int(input("Enter the element to be inserted : "))
list.insert_in_beginning(data)
elif option == 4:
data = int(input("Enter the element to be inserted : "))
list.insert_at_end(data)
elif option == 5:
data = int(input("Enter the element to be inserted : "))
x = int(input("Enter the element after which to insert : "))
list.insert_after(data, x)
elif option == 6:
data = int(input("Enter the element to be inserted : "))
x = int(input("Enter the element before which to inserted : "))
list.insert_before(data, x)
elif option == 7:
list.delete_first_node()
elif option == 8:
list.delete_last_node()
elif option == 9:
data = int(input("Enter the element to be deleted : "))
list.delete_node(data)
elif option == 10:
list.reverse_list()
elif option == 11:
break    else:
print("Wrong option")
print()```