Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
308 views
in Technique[技术] by (71.8m points)

python - logging setLevel, how it works

In the logging howto documentation there is this example:

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)

Why I should set the level to logging.DEBUG twice, for Logger, and for the StreamHandler?

I understand ch.setLevel(logging.DEBUG) will set the debug level for the stream handler. But what the effect is of setting the level to logger? Where this level is reflected?

I get the same console output if I change the level to, for example, INFO either to the Logger or to the StreamHandler.

That is:

...........
logger.setLevel(logging.INFO)
............
ch.setLevel(logging.DEBUG)

gives the same output in console than

...........
logger.setLevel(logging.DEBUG)
............
ch.setLevel(logging.INFO)
See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

It's there for fine-tuning (you can have multiple handlers, and each could have different levels set) — you can safely not set level on the handler, which will cause it to process all messages (a.k.a. NOTSET level), and leave level filtering to the logger.

Logger is also the first to filter the message based on a level — if you set the logger to INFO, and all handlers to DEBUG, you still won't receive DEBUG messages on handlers — they'll be rejected by the logger itself. If you set logger to DEBUG, but all handlers to INFO, you won't receive any DEBUG messages either — because while the logger says "ok, process this", the handlers reject it (DEBUG < INFO).


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...