定义一个栈（Stack）类 用于模拟一种具有后进先出（LIFO）特性的数据结构

class Stack:def __init__(self, stack):self.stack = []for x in stack:self.push(x)def isEmpty(self):return not self.stackdef push(self, obj):self.stack.append(obj)def pop(self):if not self.stack:print("当前栈为空")else:self.stack.pop()def top(self):if not self.stack:print("当前栈为空")else:print(self.stack[-1])def bottom(self):if not self.stack:print("当前栈为空")else:print(self.stack[0])