Python標準庫 - logging

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編寫代碼時, 常要跟蹤下其運行過程, 記錄日誌是常用的方式. 較簡單的就是print命令列印到終端, 或通過open函數寫入檔案. 但隨著代碼量的增加, 該方式不可控的弊端, 也凸顯出來, 這也正是logging模組出現的背景.

對於logging模組, 簡單來說直接import進來, 就可以用了.

In [1]: import logging

In [2]: logging.warning('Watch out!')

WARNING:root:Watch out!

In [3]: logging.info('I told you so')

In [4]:

In [4]:

第二個語句沒有輸出呢, 這需瞭解下日誌等級的概念. logging模組預設的日誌等級是WARNING, 大於該等級的日誌才會輸出, 細節如下.

Level	When it’s used
DEBUG	Detailed information, typically of interest only when diagnosing problems.
INFO	Confirmation that things are working as expected.
WARNING	An indication that something unexpected happened, or indicative of some problem in the near future (e.g. ‘disk space low’). The software is still working as expected.
ERROR	Due to a more serious problem, the software has not been able to perform some function.
CRITICAL	A serious error, indicating that the program itself may be unable to continue running.

藉助basicConfig方法, 可對日誌記錄做些配置.

In [1]: import logging

In [2]: logging.basicConfig(filename='/tmp/example.log',level=logging.DEBUG)

In [3]: logging.debug('This message should go to the log file')

In [4]: logging.info('So should this')

In [5]: logging.warning('And this, too')

$ cat /tmp/example.log

DEBUG:root:This message should go to the log file

INFO:root:So should this

WARNING:root:And this, too

在指令碼中, 可按照下面的方式使用logging模組.

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# myapp.py

import logging

import mylib

def main():

    logging.basicConfig(filename='myapp.log', format='%(asctime)s - %(name)s - %(levelname)s - %(pathname)s - %(message)s', level=logging.INFO)

    logging.info('Started')

    mylib.do_something()

    logging.info('Finished')

if __name__ == '__main__':

    main()

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# mylib.py

import logging

def do_something():

    logging.info('Doing something')

$ python myapp.py

$ cat myapp.log

2018-01-19 17:00:14,821 - root - INFO - myapp.py - Started

2018-01-19 17:00:14,821 - root - INFO - /home/zz/stage/mylib.py - Doing something

2018-01-19 17:00:14,821 - root - INFO - myapp.py - Finished

簡單瞭解了logging模組的使用, 接著看下其中幾個重要的概念.

1. Logger 日誌記錄器, 暴露給應用程式直接使用的介面, 幾個方法用於設定記錄器.

Logger.setLevel() - 指定日誌記錄器處理的日誌最低層級.

Logger.addHandler(), Logger.removeHandler() - 為日誌記錄器添加, 或移除處理器.

2. Handler 處理器, 將記錄器擷取的日誌, 傳送到其定義的目的地, 也有幾個方法設定處理器.

setLevel() - 指定處理器處理的日誌最低層級.

setFormatter() - 為處理器選擇一個格式化器.

3. Formatter 格式化器, 指定日誌的輸出格式.

最開始說了logging模組的簡單用法, 以及瞭解了上面的概念後, 看下開發較大應用時, 如何使用logging呢.

這主要介紹兩種方式, 其一是, 將logging模組的配置直接寫在應用代碼中, 如下所示.

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# simple_logging_module.py

import logging

# create logger

logger = logging.getLogger('simple_example')

logger.setLevel(logging.DEBUG)

# create console handler and set level to debug

ch = logging.StreamHandler()

ch.setLevel(logging.DEBUG)

# create formatter

formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')

# add formatter to ch

ch.setFormatter(formatter)

# add ch to logger

logger.addHandler(ch)

# 'application' code

logger.debug('debug message')

logger.info('info message')

logger.warn('warn message')

logger.error('error message')

logger.critical('critical message')

$ python simple_logging_module.py

2018-01-19 21:41:58,180 - simple_example - DEBUG - debug message

2018-01-19 21:41:58,180 - simple_example - INFO - info message

2018-01-19 21:41:58,180 - simple_example - WARNING - warn message

2018-01-19 21:41:58,180 - simple_example - ERROR - error message

2018-01-19 21:41:58,180 - simple_example - CRITICAL - critical message

其二, 配置資訊寫入檔案中, 藉助fileConfig方法載入該檔案, 如下所示.

#!/usr/bin/env python

# -*- coding: utf-8 -*-

# simple_logging_config.py

import logging

import logging.config

logging.config.fileConfig('logging.conf')

# create logger

logger = logging.getLogger('simpleExample')

# 'application' code

logger.debug('debug message')

logger.info('info message')

logger.warn('warn message')

logger.error('error message')

logger.critical('critical message')

# logging.conf

[loggers]

keys=root,simpleExample

[handlers]

keys=consoleHandler

[formatters]

keys=simpleFormatter

[logger_root]

level=DEBUG

handlers=consoleHandler

[logger_simpleExample]

level=DEBUG

handlers=consoleHandler

qualname=simpleExample

propagate=0

[handler_consoleHandler]

class=StreamHandler

level=DEBUG

formatter=simpleFormatter

args=(sys.stdout,)

[formatter_simpleFormatter]

format=%(asctime)s - %(name)s - %(levelname)s - %(message)s

datefmt=

$ python simple_logging_config.py

2018-01-19 21:53:46,216 - simpleExample - DEBUG - debug message

2018-01-19 21:53:46,216 - simpleExample - INFO - info message

2018-01-19 21:53:46,216 - simpleExample - WARNING - warn message

2018-01-19 21:53:46,216 - simpleExample - ERROR - error message

2018-01-19 21:53:46,216 - simpleExample - CRITICAL - critical message

最後簡單說下, 如何總結一個模組, 可圍繞下面三點進行說明.

1. 該模組解決的問題, 其它方法是如何做的.

2. 模組的使用, 以及核心概念(或定義).

3. 核心API的梳理.

若感興趣可關注訂閱號”資料庫最佳實務”(DBBestPractice).

Python標準庫 - logging