Python logging stdout and stderr based on level

Question

Using Python 3 logging, how can I specify that logging.debug() and logging.info() should go to stdout and logging.warning() and logging.error() go to stderr ?

Answer 1

You can create separate loggers for each stream like this:

import logging
import sys

logging.basicConfig(format="%(levelname)s %(message)s")

stdout_logger = logging.Logger(name="stdout_logger", level=logging.DEBUG)
stderr_logger = logging.Logger(name="stderr_logger", level=logging.DEBUG)

stdout_handler = logging.StreamHandler(stream=sys.stdout)
stderr_handler = logging.StreamHandler(stream=sys.stderr)

stdout_logger.addHandler(hdlr=stdout_handler)
stderr_logger.addHandler(hdlr=stderr_handler)

stdout_logger.info("this will output to stdout")
stderr_logger.info("this will output to stderr")

Then if you want to log something on 'debug' or 'info' level you can just use stdout_logger. For 'warning' and 'error' level messages use stderr_logger.

Answer 2

How to do this kind of thing is documented in the logging cookbook , and though the example levels/destinations in the cookbook recipe are slightly different from those in your question, there should be enough information there for you to arrive at a solution. The key thing is using a filter function and attaching it to a handler.