How to use python's logging to log to the screen and to a file

Question

I want to log using python's logging to both the screen and a file

this is how I log to the screen:

import logging
logging.basicConfig(level=logging.DEBUG)    
logging.debug('hello')

and this is how I log to a file:

import logging
logging.basicConfig(level=logging.DEBUG,filename='a.log')   
logging.debug('hello2')

Is there a way to log to both the file and the screen? preferably using logging.basicConfig

I am using python 2.7.14

Here: https://stackoverflow.com/questions/9321741/printing-to-screen-and-writing-to-a-file-at-the-same-time?utm_medium=organic&utm_source=google_rich_qa&utm_campaign=google_rich_qa — Shoo Limberger, Mar 29 '18 at 17:50
Its not a basic config but there are easy ways to configure in the [docs](https://docs.python.org/2/library/logging.config.html) — tdelaney, Mar 29 '18 at 17:53
Does this answer your question? [Printing to screen and writing to a file at the same time](https://stackoverflow.com/questions/9321741/printing-to-screen-and-writing-to-a-file-at-the-same-time) — mouse_freak, Feb 20 '21 at 17:08

Mattwmaster58 · Accepted Answer · 2018-03-29T19:01:18.967

10

If you want one logger for the screen and one for the log file, try this:

import logging


log = logging.getLogger('logger')
log.setLevel(logging.DEBUG)

formatter = logging.Formatter('%(message)s')

fh = logging.FileHandler('test.log', mode='w', encoding='utf-8')
fh.setLevel(logging.DEBUG)
fh.setFormatter(formatter)
log.addHandler(fh)

ch = logging.StreamHandler()
ch.setLevel(logging.INFO)
ch.setFormatter(formatter)
log.addHandler(ch)

This creates two log handlers. When you call log.debug/info/warning etc, it will log to each of your handlers. If the level they are set at is the same or higher, it will log the message, otherwise it won't.

In this example calling log.debug("test message") will save the str "test message to test.log, but you will not see the output on the screen because the StreamHandler()'s level is above the debug debug.

When you call log.info("test message"), it will save the str "test message to test.log and output it to the console because StreamHandler()'s level is info

log.setLevel(logging.DEBUG) ensures that everything will be logged. If you exclude this line, the default of WARNING will be enforced, and even if you set the level lower in a separate handler, you won't be able to log anything >= that level

The levels for logging are as follows:

DEBUG
INFO
WARNING
ERROR
CRITICAL

edited Mar 29 '18 at 19:01

answered Mar 29 '18 at 17:54

Mattwmaster58

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I copied your code, added at the end this line: log.info('test') and nothing happend – Goolmoos Mar 29 '18 at 18:37
it printed this: test3 and in the next line: DEBUG:logger:test3 – Goolmoos Mar 29 '18 at 18:59
@Goolmoos this question is turning out to be harder than I thought. The last edit I made should do it. – Mattwmaster58 Mar 29 '18 at 19:00
FYI: just tested with python 3.7.2 and it works perfectly. Thanks. – Maxence Bouvier Jun 30 '21 at 09:24
Tried on Python 3.8 and it works nice. However, I see that the output file becomes readable only after the script has finished, I would need to access it also while the execution is ongoing (i.e. with Tail command). Is that possible? – Max1234-ITA Nov 09 '22 at 16:22

score 3 · Answer 2 · answered Mar 29 '18 at 19:17

I succeeded. here is my code:

import logging
formatter = logging.Formatter('%(message)s')
logging.getLogger('').setLevel(logging.DEBUG)
fh = logging.FileHandler('a.log')
fh.setLevel(logging.DEBUG)
fh.setFormatter(formatter)
logging.getLogger('').addHandler(fh)
ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG)
ch.setFormatter(formatter)  
logging.getLogger('').addHandler(ch)
logging.debug('debug message')

How to use python's logging to log to the screen and to a file

2 Answers2