Pass a Python ArgumentParser to another module?

Question

I have this Python code in main.py:

parser = argparse.ArgumentParser()
parser.add_argument("subname", help="Name of subreddit")
args = parser.parse_args()

Then in another file speciallogger.py:

import logging
import time

from logging.handlers import TimedRotatingFileHandler
path='logs/log_SUBNAMEHERE_logger.txt'
logmsg = logging.getLogger("Rotating Log")
fmt = u'%(asctime)s\t%(levelname)s\t%(filename)s:%(lineno)d\t%(message)s'
logmsg.setLevel(logging.INFO)
handler = TimedRotatingFileHandler(path, when="d", interval=1, backupCount=14)
handler.setFormatter(logging.Formatter(fmt))
logmsg.addHandler(handler)

The script (starts with main.py) executes via a cron using an argument.

I need to pass that argument to speciallogger.py so I can name the filename what subname is, along with ensuring logmsg can be used across all modules without the log file being recreated each import during a script using multiple modules.

How can I do this?

Zeno · Accepted Answer · 2019-10-19 05:29:24Z

1

Make a function in speciallogger.py and call that function right after doing the arg parsing.

speciallogger.py

import logging
import time
from logging.handlers import TimedRotatingFileHandler

def initialize(subname):
    path = f'logs/log_{subname}_logger.txt'
    logmsg = logging.getLogger("Rotating Log")
    fmt = u'%(asctime)s\t%(levelname)s\t%(filename)s:%(lineno)d\t%(message)s'
    logmsg.setLevel(logging.INFO)
    handler = TimedRotatingFileHandler(path, when="d", interval=1, backupCount=14)
    handler.setFormatter(logging.Formatter(fmt))
    logmsg.addHandler(handler)

main.py

import speciallogger
...
if __name__ == "__main__":
    ...
    parser = argparse.ArgumentParser()
    parser.add_argument("subname", help="Name of subreddit")
    args = parser.parse_args()
    speciallogger.initialize(args.subname)

logging.getLogger() will return the same logger object no matter where in the program it's called, per the documentation:

"All calls to this function with a given name return the same logger instance. This means that logger instances never need to be passed between different parts of an application."

Thus, when you modify it by doing setLevel and addHandler, you're making a persistent change that should reflect across the entire program.

edited Oct 19, 2019 at 5:29

Zeno

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answered Oct 18, 2019 at 3:49

Green Cloak Guy

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2 Comments

Zeno Over a year ago

I've tried this, but in main.py it gives the error NameError: name 'logging' is not defined. How am I meant to log lines in main.py?

Green Cloak Guy Over a year ago

@Zeno you would log things the same way as before. Import logging and use it as normal (call getLogger("Rotating Log") to make sure that you're using the same logger you modified during initialization).

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