class Node:
   def __init__(self, data):
      self.data = data
      self.next = None
      self.prev = None

class DoublyLinkedList_structure:
   def __init__(self):
      self.first = None
      self.last = None

   def add_vals(self, data):
      self.insert_at_end(Node(data))

   def insert_at_end(self, newNode):
      if self.last is None:
         self.last = newNode
         self.first = newNode
      else:
         newNode.prev = self.last
         self.last.next = newNode
         self.last = newNode

def find_largest_val(my_list):
   if my_list.first is None:
      return None
   largest_val = my_list.first.data
   curr = my_list.first.next
   while curr:
      if curr.data > largest_val:
         largest_val = curr.data
      curr = curr.next
   return largest_val

my_instance = DoublyLinkedList_structure()

my_list = input('Enter the elements in the doubly linked list ').split()
for elem in my_list:
   my_instance.add_vals(int(elem))

largest_val = find_largest_val(my_instance)
if largest_val:
   print('最大值为{}。'.format(largest_val))
else:
   print('列表为空。')

输入双向链表中的元素45 12 67 89 234 567 888 44 999
最大值为999。