StackNode

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

    def __str__(self):
        return str(self.data)

class LinkStack:
    def __init__(self):
        self.top = None

# 进栈
    def Push(self,e):
        p=StackNode(e)
        p.next=self.top
        self.top=p

# 出栈
    def Pop(self):
        if self.top is None:
            raise Exception("栈空")
        e=self.top.data
        self.top=self.top.next
        return e

# 读取栈顶元素
    def get_top(self):
        if self.top is not None:
            return self.top.data
        else:
            raise Exception("栈空")

# 求长度
    def __len__(self):
        p=self.top
        count=0
        while p.next is not None:
            p=p.next
            count+=1
        return count

if __name__ == '__main__':
    s=LinkStack()
    s.Push(10)
    s.Push(11)
    s.Push(12)
    # print("栈为：",s)
    print("栈的长度为：",len(s))
    print("此时栈顶元素为：",s.get_top())