Python logger 没打出行数

# !/user/bin/python
# -*- coding: utf-8 -*-
'''
subprocess : 需要在linux平台上测试 shell
logging
'''

import logging
# 将日志输出在文件里
# logging.basicConfig(filename="app.log", level=logging.DEBUG)
logging.basicConfig(filename="app.log",
                    level=logging.WARNING,
                    format='%(asctime)s %(levelname)s  %(filename)s:%(lineno)d  - %(message)s',
                    datefmt='%m/%d/%Y %I:%M:%S %p')  # 在日志上加上时间. %p代表pm.  TODO 为什么没打出行数?