class Node:  
   def __init__(self,data):  
      self.data = data
      self.next = None  
   
class list_creation:  
   def __init__(self):  
      self.head = Node(None)  
      self.tail = Node(None)  
      self.head.next = self.tail  
      self.tail.next = self.head  
      self.size = 0;  

   def add_data(self,my_data):  
      new_node = Node(my_data)
      if self.head.data is None:  
       self.head = new_node  
       self.tail = new_node  
       new_node.next = self.head  
      else:  
         self.tail.next = new_node
         self.tail = new_node
         self.tail.next = self.head
      self.size = self.size+1

   def add_in_between(self,my_data):  
      new_node = Node(my_data);  
      if(self.head == None):  
         self.head = new_node;  
         self.tail = new_node;  
         new_node.next = self.head;  
      else:  
         count = (self.size//2) if (self.size % 2 == 0) else ((self.size+1)//2);  
         temp = self.head;  
         for i in range(0,count):  
            curr = temp;  
            temp = temp.next;  
         curr.next = new_node;  
         new_node.next = temp;  
      self.size = self.size+1;
         
   def print_it(self):  
      curr = self.head;  
      if self.head is None:  
         print("列表为空");  
         return;  
      else:
         print(curr.data)
         while(curr.next != self.head):  
            curr = curr.next;  
            print(curr.data)
         print("\n");  
   
class circular_linked_list:  
   my_cl = list_creation()
   print("正在添加节点到列表中")
   my_cl.add_data(21)
   my_cl.add_data(54)
   my_cl.add_data(78)
   my_cl.add_data(99)
   print("列表是：")
   my_cl.print_it();  
   my_cl.add_in_between(33);
   print("更新后的列表是：")
   my_cl.print_it();  
   my_cl.add_in_between(56);
   print("更新后的列表是：")
   my_cl.print_it();  
   my_cl.add_in_between(0);
   print("更新后的列表是：")
   my_cl.print_it();   

正在添加节点到列表中
列表是：
21
54
78
99

更新后的列表是：
21
54
33
78
99

更新后的列表是：
21
54
33
56
78
99

更新后的列表是：
21
54
33
0
56
78
99