1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3  4  5 class StackUnderflow(ValueError): 6     pass 7  8 #链表节点 9 class Node(object):10     def __init__(self, elem, next_ = None):11         self.elem = elem12         self.next = next_13 14 #顺序表实现栈15 class SStack(object):16     def __init__(self):17         self._elems = []18 19     def is_empty(self):20         return self._elems == []21 22     def top(self):23         if self.is_empty():24             raise StackUnderflow25         return self._elems[-1]26 27     def push(self, elem):28         self._elems.append(elem)29 30     def pop(self):31         if self.is_empty():32             raise StackUnderflow33         return self._elems.pop()34 35 #链表实现栈36 class LStack(object):37     def __init__(self):38         self._top = None39 40     def is_empty(self):41         return self._top is None42 43     def top(self):44         if self.is_empty():45             raise StackUnderflow("in LStack.top()")46         return self._top.elem47 48     def push(self, elem):49         self._top = Node(elem, self._top)50 51     def pop(self):52         if self.is_empty():53             raise StackUnderflow("in LStack.pop()")54         result = self._top.elem55         self._top = self._top.next56         return result57 58 59 60 if __name__=="__main__":61     st1 = SStack()62     st1.push(3)63     st1.push(5)64     while not st1.is_empty():65         print(st1.pop())66 67     print("============")68     st2 = LStack()69     st2.push(3)70     st2.push(5)71     while not st2.is_empty():72         print(st2.pop())