直接看程式碼，有詳細註解

class Node(object):
    """節點"""
    def __init__(self, elem):
        self.elem = elem
        self.next = None


class SingleCycleLinkList(object):
    """單向迴圈連結串列"""
    def __init__(self, node=None):
        self.__head = node
        if node:
            node.next = node

    def is_empty(self):
        """連結串列是否為空"""
        return self.__head == None

    def length(self):
        """連結串列長度"""
        if self.is_empty():
            return 0
        # cur遊標，用來移動遍歷節點
        cur = self.__head
        # count記錄數量
        count = 1
        while cur.next != self.__head:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍歷整個連結串列"""
        if self.is_empty():
            return
        cur = self.__head
        while cur.next != self.__head:
            print(cur.elem, end=" ")
            cur = cur.next
        # 退出迴圈，cur指向尾節點，但尾節點的元素未列印
        print(cur.elem)

    def add(self, item):
        """連結串列頭部新增元素，頭插法"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = node
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            # 退出迴圈，cur指向尾節點
            node.next = self.__head
            self.__head = node
            # cur.next = node
            cur.next = self.__head

    def append(self, item):
        """連結串列尾部新增元素, 尾插法"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
            node.next = node
        else:
            cur = self.__head
            while cur.next != self.__head:
                cur = cur.next
            # node.next = cur.next
            node.next = self.__head
            cur.next = node

    def insert(self, pos, item):
        """指定位置新增元素
        :param  pos 從0開始
        """
        if pos <= 0:
            self.add(item)
        elif pos > (self.length()-1):
            self.append(item)
        else:
            pre = self.__head
            count = 0
            while count < (pos-1):
                count += 1
                pre = pre.next
            # 當迴圈退出後，pre指向pos-1位置
            node = Node(item)
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        """刪除節點"""
        if self.is_empty():
            return

        cur = self.__head
        pre = None

        while cur.next != self.__head:
            if cur.elem == item:
                # 先判斷此結點是否是頭節點
                if cur == self.__head:
                    # 頭節點的情況
                    # 找尾節點
                    rear = self.__head
                    while rear.next != self.__head:
                        rear = rear.next
                    self.__head = cur.next
                    rear.next = self.__head
                else:
                    # 中間節點
                    pre.next = cur.next
                return
            else:
                pre = cur
                cur = cur.next
        # 退出迴圈，cur指向尾節點
        if cur.elem == item:
            if cur == self.__head:
                # 連結串列只有一個節點
                self.__head = None
            else:
                # pre.next = cur.next
                pre.next = self.__head

    def search(self, item):
        """查詢節點是否存在"""
        if self.is_empty():
            return False
        cur = self.__head
        while cur.next != self.__head:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        # 退出迴圈，cur指向尾節點
        if cur.elem == item:
            return True
        return False


if __name__ == "__main__":
    ll = SingleCycleLinkList()
    print(ll.is_empty())
    print(ll.length())

    ll.append(1)
    print(ll.is_empty())
    print(ll.length())


    ll.append(2)
    ll.add(8)
    ll.append(3)
    ll.append(4)
    ll.append(5)
    ll.append(6)
    # 8 1 2 3 4 5 6