如何将python logging.debug（）消息输出到标准输出？

Question

I have a script that gives me messages through the python logging module: logging.debug("a message here") . Yet when I run the linux command python3 myscript.py -v >> log.txt I get a blank file. How can I get the debug messages to output to the log file?

Answer 1

By default, the logging module logs to sys.stderr . Capture stream 2, stderr instead:

python3 myscript.py -v 2>> log.txt

You can also redirect both stdin and stderr to the same file:

python3 myscript.py -v >> log.txt 2>&1

Here stderr is sent to the same output stdin (output 1) is directed to.

This is assuming you already set the logging level to allow for level DEBUG messages.

Last but not least, you can tell logging.basicConfig() to log to a different stream instead of stderr :

logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)

or you can give it a filename, that way no redirection is needed:

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

Answer 2

Set your log level to be on debug.

Logger.setLevel(Logger.DEBUG)

See the docs for logging wherein they state:

Sets the threshold for this logger to lvl. Logging messages which are less severe than lvl will be ignored. When a logger is created, the level is set to NOTSET (which causes all messages to be processed when the logger is the root logger, or delegation to the parent when the logger is a non-root logger). Note that the root logger is created with level WARNING.