In the previous exercise checkpoint, you may have noticed that when we attempted to add DEBUG messages to our calculator application, they didn’t appear in the console. What’s going on here?

Well, each logger object has a default set of log levels that will output unless a different log level is explicitly set. When we set a log level for a logger, any log message that has this log level and higher will output. The default log level is WARNING in Python’s logging module.

We used the default WARNING level in the previous exercise, so only log messages with WARNING level or higher were processed and logged to the console.

To change the default log level for a logger, we can use a method called setLevel(level). The level parameter represents the numeric value of the log level to use. If we want the DEBUG message to show from our previous exercise checkpoint, we can use the setLevel(level) method like below:

logger.setLevel(logging.DEBUG)

This will set our log level to DEBUG and allow all log messages with a severity of DEBUG or higher to log to the console.

There are several cases where setting the log level can be helpful. If we are trying to troubleshoot a problem within our application that is causing it to crash, it would be optimal to see only the CRITICAL level log messages and filter out all other messages.

If we are still in a development phase of our application and have to debug often, setting the log level to DEBUG is useful for obtaining helpful debugging log messages. Once our application is ready for deployment, we can easily set the log level to WARNING to filter out developer-friendly information like DEBUG and INFO messages.