FileHandler double logs string in a file

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import logging


logger = logging.getLogger(__name__)
logger.addHandler(logging.FileHandler(filename='logloglog.log'))
logger.critical('A!')

for handler in logger.handlers:
    handler.close()

logger.addHandler(logging.FileHandler(filename='logloglog.log'))
logger.critical('B!')

I am trying to understand why the above code logs B! string in logloglog.log file twice. It confuses me, since I log both A! and B! only one time. Can you help me?

python-logging python
2 Answers

logger.addHandler was called twice, so there are two file handlers (pointing at the same filename):

>>> logger.handlers
[<FileHandler /home/wglenn/git/modules/logloglog.log (NOTSET)>,
 <FileHandler /home/wglenn/git/modules/logloglog.log (NOTSET)>]

By the time logger.critical('B!') is called, each handler will write out the event once.

It does not matter that you've closed handlers earlier, logging will just re-open the resource when it needs to emit, if necessary.

user_6740390

When a new log message arrives the file handler will automatically reopen the file. so

for handler in logger.handlers:
    handler.close()
    logger.removeHandler(handler) // add this line.

see the ref.

user_17530730
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