用Python实现栈---1顺序表

class Stack:
    def __init__(self):
        self.__data = []
        #把列表的最后一个元素作为栈顶
    def push(self, item):
        self.__data.append(item)

    def pop(self):
        if self.is__empty():
            raise ValueError("栈为空")
        return self.__data.pop()

    def top(self):#返回栈顶元素
        if self.is__empty():
            raise ValueError("栈为空")
        return self.__data[-1]

    def is__empty(self):
        return self.__data == []


    def size(self):
        return len(self.__data)

if __name__ == '__main__':
    stack = Stack()
    stack.push(1)
    stack.push(2)
    stack.push(3)
    stack.push(4)
    print(stack.pop())
    print(stack.pop())
    print(stack.pop())
    print(stack.pop())
    print(stack.pop())