题解 | 【模板】队列操作

import sys

input = sys.stdin.readline  #引用readline 读取数据时一行行进行读取

class stackOperate(object):
    def __init__(self):
        self.stacklist = []
    
    def operateStep(self,arr):
        if arr[0] == '1' :
            self.stacklist.append(arr[1])
        if arr[0] == '2' :
            if self.stacklist :
                self.stacklist.pop(0)
            else :
                print('ERR_CANNOT_POP')
        if arr[0] == '3' :
            if self.stacklist :
                print(self.stacklist[0])
            else :
                print('ERR_CANNOT_QUERY')
        if arr[0] == '4' :
            print(len(self.stacklist))

if __name__ == '__main__':
    res = stackOperate()
    n = int(input())
    for _ in range(n):
        para = input().split()  #将每一行的数据拆分成列表，传入函数
        res.operateStep(para)