A Brief Digression About Logging

A Brief Digression About Logging

Logging is an interesting subject. For most developers, most of the time, we don’t think too hard about logging. Maybe we’ve got some coding standards that mandate some minimal level of logging, but otherwise we’re just not concerned about how we log. But one day you’ll find yourself five hours into a marathon debugging session, throwing print statements in random places and thinking to yourself “If only I’d put in some logging here, I’d have some idea of what was going on in this system!”

So you turn to the Python logging, open the docs and recoil in horror. All you want to do is log things! What’s this nonsense about loggers, and handlers, and LogRecords?

It’s OK, I’m here to help.

My Advice? Ignore It All.

The logging module is incredibly powerful, but as a result it’s also incredibly complicated. The reality is, most of us will never need to touch its complexity.

Here’s my promise. The following lines of code will solve 95% of your logging problems.


When you’re writing a library and you want it to log, here’s what you do. Find your top-level __init__.py file and add the following two lines to it:

import logging

This essentially enables the default logging behaviour: do nothing.

Then, in each file where you want to emit logs, add this line at the top:

log = logging.getLogger(__name__)

That’s it, you’re done. Seriously. To log, you now just call the logging methods: log.debug(), log.info(), log.warning(), log.error() and log.critical(), depending on the severity of log you want.

Applications and Executables

What if you’re an application developer, or you’re writing the top-level script? You know your libraries are logging, and you are too, but how do you turn it on? Easy:

import logging

That’s it. Done. You’ll now get your default logging to stderr. Want to put it somewhere else, or log at a different level? Here are the docs. Some highlights are logging at a specific level (logging.basicConfig(level=logging.DEBUG)) and logging to file (logging.basicConfig(filename='myapp.log')).

That’s it.


Remember, never use the root logger. Always call .debug() and friends on a logger you got by calling logging.getLogger(__name__).

Otherwise, there’s really nothing else. If you need anything else in the logging library, you probably already understand it.

See? Logging is easy.

EDIT (31/05/2014): Note that the NullHandler is only available on Python 2.7 or later. If you want an equivalent for Python 2.6, use this to provide a fallback:

class NullHandler(logging.Handler):
    def emit(self, record):