How to limit log file size in python

Question

I am using windows 7 and python 2.7. I want to limit my log file size to 5MB. My app, when it starts, writes to log file, and then the app terminates. When my app starts again, it will write in same log file. So app is not continuously running. App initiates, processes and terminates.

My code for logging is:

import logging
import logging.handlers
logging.basicConfig(filename=logfile.log, level="info", format='%(asctime)s %(levelname)s %(funcName)s(%(lineno)d) %(message)s')
logging.info("*************************************************")

I tried with RotatingFileHandler but it didn't work

logging.handlers.RotatingFileHandler(logFile, mode='a', maxBytes=5*1024*1024, backupCount=2, encoding=None, delay=0)

So, how can I enforce a file size limit in python?

RotatingFileHandler is a way to go. How exactly it didn't work? — J0HN, Jul 01 '14 at 07:58
may be because app is not continuosly running or is there any wrong in coding — imp, Jul 01 '14 at 07:59
That doesn't answer my question :) I'm not asking you to speculate on why it's so, but WHAT exactly is wrong with RotatingFileHandler. Errors, exceptions, crashes, anything? Does it write to log at all? — J0HN, Jul 01 '14 at 08:06
@imp it doesn't matter how many times it gets interrupted. See [getLogger](https://docs.python.org/2/library/logging.html?highlight=logging#logger-objects). It will always return a reference to the same logger — Shadow9043, Jul 01 '14 at 08:19

score 103 · Accepted Answer · edited Sep 17 '20 at 13:16

103

Lose basicConfig() and use RotatingFileHandler:

import logging
from logging.handlers import RotatingFileHandler

log_formatter = logging.Formatter('%(asctime)s %(levelname)s %(funcName)s(%(lineno)d) %(message)s')

logFile = 'C:\\Temp\\log'

my_handler = RotatingFileHandler(logFile, mode='a', maxBytes=5*1024*1024, 
                                 backupCount=2, encoding=None, delay=0)
my_handler.setFormatter(log_formatter)
my_handler.setLevel(logging.INFO)

app_log = logging.getLogger('root')
app_log.setLevel(logging.INFO)

app_log.addHandler(my_handler)

while True:
    app_log.info("data")

edited Sep 17 '20 at 13:16

betontalpfa

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answered Jul 01 '14 at 08:09

Shadow9043

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just work in current py file ,how to make it work in other py files – geosmart Jan 10 '20 at 02:25
@geosmart `logging.getLogger('root').info('some log')` in any python file should work – Alex Dec 28 '21 at 17:19
1

For Python 3, don't forget to update the delay flag from 0 to False. It may appear like an integer but it is actually a boolean parameter. – Vishal Rangras May 31 '22 at 11:09

score 19 · Answer 2 · edited Dec 15 '19 at 13:54

When you use logging.basicConfig with a file, the log is attached with a file handler to handle writing to the file. afterwards you created another file handler to the same file with logging.handlers.RotatingFileHandler

Now, once a rotate is needed, RotatingFileHandler is trying to remove the old file but it can't becuase there is an open file handler

this can be seen if you look directly at the log file handlers -

import logging
from logging.handlers import RotatingFileHandler

log_name = 'c:\\log.log'
logging.basicConfig(filename=log_name)
log = logging.getLogger()
handler = RotatingFileHandler(log_name, maxBytes=1024, backupCount=1)
log.addHandler(handler)


[<logging.FileHandler object at 0x02AB9B50>, <logging.handlers.RotatingFileHandler object at 0x02AC1D90>]

score 16 · Answer 3 · answered Aug 05 '20 at 14:47

To use BasicConfig and RotatingFileHandler, add RotatingFileHandler as Handler in BasicConfig.

main.py:

import logging

rfh = logging.handlers.RotatingFileHandler(
    filename='foo.log', 
    mode='a',
    maxBytes=5*1024*1024,
    backupCount=2,
    encoding=None,
    delay=0
)

logging.basicConfig(
    level=logging.DEBUG,
    format="%(asctime)s %(name)-25s %(levelname)-8s %(message)s",
    datefmt="%y-%m-%d %H:%M:%S",
    handlers=[
        rfh
    ]
)

logger = logging.getLogger('main')

logger.debug("test")

other.py

import logging

class Other():
    def __init(self):
        self.logger = logging.getLogger('other')
        self.logger.info("test2")

"test" will be written into foo.log with the tag 'main'

"test2" will be written into foo.log with the tag 'other'

No writes to foo.log happen for me ( – Nazar Apr 03 '21 at 19:57 — Nazar, Apr 03 '21 at 19:57

How to limit log file size in python

3 Answers3

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