Python链栈的实现

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


class Stack(object):
    def __init__(self):
        self.node = Node(None)
        self.head = self.node
        self.size = 0

    def is_empty(self):
        return self.size == 0

    def get_size(self):
        return self.size

    def push(self, data):
        node = Node(data)
        node.next = self.head.next
        self.head.next = node
        self.size += 1

    def pop(self):
        if not self.is_empty():
            current_node = self.head.next
            if self.get_size() == 1:
                self.head.next = None
            else:
                self.head.next = self.head.next.next
            self.size -= 1
            return current_node.data
        else:
            raise IndexError("pop from empty stack")

    def top(self):
        if not self.is_empty():
            return self.head.next.data
        else:
            raise IndexError("stack is empty")


s = Stack()
s.push(1)
s.push(2)
print(s.get_size())
s.pop()
print(s.get_size())