Python按照重要程度把日誌分爲5個級別，如下：
| 級別 | 日誌函數 | 描述 |
|---|---|---|
| DEBUG | logging.debug() | 最低級別，追蹤問題時使用 |
| INFO | logging.info() | 記錄程序中一般事件的信息，或確認一切工作正常 |
| WARNING | logging.warning() | 記錄信息，用於警告 |
| ERROR | logging.error() | 用於記錄程序報錯信息 |
| CRITICAL | logging.critical() | 最高級別，記錄可能導致程序崩潰的錯誤 |
可以通過level參數，設置不同的日誌級別。當設置爲高的日誌級別時，低於此級別的日誌不再打印。
五種日誌級別按從低到高排序：
DEBUG < INFO < WARNING < ERROR < CRITICAL
1. level設置爲DEBUG級別，所有的日誌都會打印
import logging
logging.basicConfig(level=logging.DEBUG, format=' %(asctime)s - %(levelname)s -%(message)s')
logging.debug('Some debugging details.')
logging.info('The logging module is working')
logging.warning('An error message is about to be logged.')
logging.error('An error has occurred.')
logging.critical('The program is unable to recover!')
2019-11-17 15:24:30,065 - DEBUG -Some debugging details.
2019-11-17 15:24:30,074 - INFO -The logging module is working
2019-11-17 15:24:30,086 - WARNING -An error message is about to be logged.
2019-11-17 15:24:30,105 - ERROR -An error has occurred.
2019-11-17 15:24:30,107 - CRITICAL -The program is unable to recover!
2. level設置爲ERROR級別時，只顯示ERROR和CRITICAL日誌
import logging
logging.basicConfig(level=logging.ERROR, format=' %(asctime)s - %(levelname)s -%(message)s')
logging.debug('Some debugging details.')
logging.info('The logging module is working')
logging.warning('An error message is about to be logged.')
logging.error('An error has occurred.')
logging.critical('The program is unable to recover!')
2019-11-17 15:30:46,767 - ERROR -An error has occurred.
2019-11-17 15:30:46,768 - CRITICAL -The program is unable to recover!
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