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 = int(self.size)+1;  
     
   def delete_from_mid(self):  
      if(self.head == None):  
         return;  
      else:  
         count = (self.size//2) if (self.size % 2 == 0) else ((self.size+1)//2);  
         if( self.head != self.tail ):  
            temp = self.head;  
            curr = None;  
            for i in range(0, count-1):  
               curr = temp;  
               temp = temp.next;  
            if(curr != None):  
               curr.next = temp.next;  
               temp = None;  
            else:  
               self.head = self.tail = temp.next;  
               self.tail.next = self.head;  
               temp = None;  
         else:  
            self.head = self.tail = None;  
      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()  
   my_cl.add_data(11)  
   my_cl.add_data(52)  
   my_cl.add_data(36)  
   my_cl.add_data(74)
   print("原始列表是：")
   my_cl.print_it()  
   while(my_cl.head != None):  
      my_cl.delete_from_mid()
      print("更新后的列表是：")
      my_cl.print_it();

原始列表是：
11
52
36
74

更新后的列表是：
11
36
74

更新后的列表是：
11
74

更新后的列表是：
74

更新后的列表是：
列表为空