class Queue(object):    def __init__(self):        self.data_list = [] #定義一個字段（空數組）    def init_queue(self):        self.data_list = []  #初始化這個空數組    def insert(self, data):        self.data_list.append(data)    def pop(self):        if len(self.data_list) == 0:            return None        data = self.data_list[0]        del self.data_list[0]        return data    def size(self):        return len(self.data_list)queue = Queue()PRint queue.size()queue.insert(1)queue.insert(2)queue.insert(3)head = queue.pop()print headhead = queue.pop()print headhead = queue.pop()print headhead = queue.pop()print head