import os

 os.chdir("E:\\Python_temp")

 class Stack:

     def __init__(self):

         self._a = []

     def __len__(self):

         return len(self._a)

     def isEmpty(self):

         return len(self._a) == 0

     def push(self,item):

         self._a +=[item]

     def pop(self):

         self._a.pop()

 def main():

     stack = Stack()

     stack.push("a")

     stack.push("b")

     stack.push("c")

     stack.pop()

     for item in stack._a:

         print(item)

 if __name__ == "__main__": main()

输出结果：
>> a 
>> b