redirecting screen output from python logging to a file

How can I redirect the output of python logging statements to a file at run time using redirection?

I am using python 3.7 in Debian. When I redirect the output from a python script containing a print statement to a file, I get the expected result – a file containing the output.

If I use logging.debug to create the screen output and redirect this to a file, I get the output displayed on the screen and a zero size file.

python_test.py

print('hello')

python python_test.py > test.txt
more test.txt
hello

python_logging_test.py

import logging

logging.basicConfig(level=logging.DEBUG, format='%(message)s')

logging.debug('from logger')

python python_logging_test.py > test2.txt
from logger
ls -al test2.txt
-rw-r--r-- 1 bart bart 0 Mar 31 20:00 test2.txt

Answer

logging does not use the stdout stream, it uses the stderr output stream.

Redirect the stderr stream:

method 1

python python_logging_test.py 2> test2.txt

more test2.txt
from logging

method 2

Use stdbuf:

stdbuf -e L python python_logging_test.py > test2.txt

more test2.txt
from logger

from stdbuf –help -e, –error=MODE adjust standard error stream buffering If MODE is ‘L’ the corresponding stream will be line buffered.