class stack(): __data=None __next=None __length=0 def push(self,v): """进栈"""         tmp=stack()         tmp.data=v         tmp.next=self.__next         self.__next=tmp         self.__length+=1 def pop(self): """出栈"""         tmp=self.__next         self.__next=tmp.next         self.__length-=1 return tmp.data     @property def top(self): """栈顶元素""" if self.__next: return self.__next.data return None     @property def length(self): """栈的长度""" return self.__length s=stack() s.push(100) #入栈 s.push(101) #入栈 print "当前栈的长度为:",s.length print "当前出栈的元素为:",s.pop() #出栈 print "当前栈的长度为:",s.length print "当前栈顶元素为:",s.top print "当前出栈的元素为:",s.pop() #出栈 print "当前栈顶元素为:",s.top