Logger Configuration to Log to File and Print to Stdout

logger configuration to log to file and print to stdout

Just get a handle to the root logger and add the StreamHandler. The StreamHandler writes to stderr. Not sure if you really need stdout over stderr, but this is what I use when I setup the Python logger and I also add the FileHandler as well. Then all my logs go to both places (which is what it sounds like you want).

import logging
logging.getLogger().addHandler(logging.StreamHandler())

If you want to output to stdout instead of stderr, you just need to specify it to the StreamHandler constructor.

import sys
# ...
logging.getLogger().addHandler(logging.StreamHandler(sys.stdout))

You could also add a Formatter to it so all your log lines have a common header.

ie:

import logging
logFormatter = logging.Formatter("%(asctime)s [%(threadName)-12.12s] [%(levelname)-5.5s]  %(message)s")
rootLogger = logging.getLogger()

fileHandler = logging.FileHandler("{0}/{1}.log".format(logPath, fileName))
fileHandler.setFormatter(logFormatter)
rootLogger.addHandler(fileHandler)

consoleHandler = logging.StreamHandler()
consoleHandler.setFormatter(logFormatter)
rootLogger.addHandler(consoleHandler)

Prints to the format of:

2012-12-05 16:58:26,618 [MainThread  ] [INFO ]  my message

Making Python loggers output all messages to stdout in addition to log file

All logging output is handled by the handlers; just add a logging.StreamHandler() to the root logger.

Here's an example configuring a stream handler (using stdout instead of the default stderr) and adding it to the root logger:

import logging
import sys

root = logging.getLogger()
root.setLevel(logging.DEBUG)

handler = logging.StreamHandler(sys.stdout)
handler.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
handler.setFormatter(formatter)
root.addHandler(handler)

Python logging to stdout and log file

You just need to add another handler, like a logging.FileHandler

fh = logging.FileHandler(r'/path/to/log.txt')
logger.addHandler(fh)

Simplest way to set up python logging to stdout

If you just need to print the messages to the stdout, then logging.basicConfig is a handy shortcut for the configuration you listed. It will create a StreamHandler, attach the default Formatter to it and attach the handler to the root logger.

import logging

logging.basicConfig(level=logging.DEBUG, stream=sys.stdout)
logging.getLogger().info('hi')

Check out the docs for more configuration possibilities; for example,

logging.basicConfig(filename='some.log', level=logging.DEBUG)

will configure writing to file some.log instead of stdout.

Note that logging.basicConfig won't do a thing if the logger is already configured (meaning that there are handlers attached to the root logger already). So this code:

import logging

logging.getLogger().addHandler(logging.FileHandler(filename='some.log'))
logging.basicConfig(level=logging.DEBUG)

will not configure logging to stdout anymore; you will have to do it yourself.

How to log outputs and errors to file without knowing where errors will occur

Found the answer myself: just type this in the terminal and make sure that you have a log.text file in the right directory. No changes in the script needed.

python script.py &> ./log.txt

Inspired from this question: Redirect stdout and stderr to same file using Python

Python Logger : StreamHandler not controlling my terminal stdout?

It seems it is related to the fact that I have multiple modules - each module can have a logger to console, but the main script must remain in control and have its own logger set (which I did not have).
This page solved my problem: https://docs.python.org/3/howto/logging-cookbook.html#logging-to-multiple-destinations

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