Python logging before you run logging.basicConfig?

Question

It appears that if you invoke logging.info() BEFORE you run logging.basicConfig, the logging.basicConfig call doesn't have any effect. In fact, no logging occurs.

Where is this behavior documented? I don't really understand.

Answer 1

Yes.

You've asked to log something. Logging must, therefore, fabricate a default configuration. Once logging is configured... well... it's configured.

"With the logger object configured, the following methods create log messages:"

Further, you can read about creating handlers to prevent spurious logging. But that's more a hack for bad implementation than a useful technique.

There's a trick to this.

1. No module can do anything except logging.getlogger() requests at a global level.

2. Only the if __name__ == "__main__": can do a logging configuration.

If you do logging at a global level in a module, then you may force logging to fabricate it's default configuration.

Don't do logging.info globally in any module. If you absolutely think that you must have logging.info at a global level in a module, then you have to configure logging before doing imports. This leads to unpleasant-looking scripts.

Answer 2

You can remove the default handlers and reconfigure logging like this:

# if someone tried to log something before basicConfig is called, Python creates a default handler that
# goes to the console and will ignore further basicConfig calls. Remove the handler if there is one.
root = logging.getLogger()
if root.handlers:
    for handler in root.handlers:
        root.removeHandler(handler)
logging.basicConfig(format="'%(asctime)s %(message)s',level=logging.DEBUG)