1 class stack(): 2     def __init__(self): 3         self.stack = [] 4     def empty(self): 5         return self.stack==[] 6     def push(self,data): 7         self.stack.append(data) 8     def pop(self): 9         if self.empty():10             return None;11         else:12             return self.stack.pop(-1)13     def top(self):14         if self.empty():15             return None16         else:17             return self.stack[-1]18     def length(self):19         return len(self.stack)

class queue():    def __init__(self):        self.queue = []    def empty(self):        return self.queue == []    def enqueue(self,data):        self.queue.append(data)    def dequeue(self):        if self.empty():            return None        else:            return self.queue.pop(0)        #返回头信息和队列长度可以不实现    def head(self):        if self.empty():            return None        else:            return self.queue[0]    def length(self):        return len(self.queue)