Power-Up Your Python Logging

A guide to take you from beginner to pro with Python’s built-in logging tools

Debugging a large application sucks. Especially when you have a bug that shows itself in production but can’t be reproduced in the dev environment. Finding these can be made easier with the use of Python’s built-in logging tools.

This guide is designed to help newcomers understand Python’s logging module. Heaven knows it confused me when I first started. In the end, we will have a working logger that is able to throw errors to a discord channel.

The code for this problem can be found in the civicsoft/ieddit GitHub repository.

Quick Overview of Logging

One note before we get into logging: both loggers and handlers below use, what we call, levels. This is a hierarchy of how things are handled.

For example, when we set a handler to the DEBUG level, it will receive debug statements and all the levels above it. These levels are used to filter data by its importance.

Loggers

A logger is simply a named instance of the logging object. All loggers are “global” within your program. Here is an example of what that looks like.

We have defined a logger named app in app.py.

# ieddit/app.py
import logging
logger = logging.getLogger("app")

Now, if we wanted to, we could drop into another file and have access to that same logger instance we created before.

This is what that would look like:

# ieddit/utils.py
import logging
logger = logging.getLogger("app")

Now the utils.py has access to that same logger instance! This means that we can declare all the loggers we want before they are ever needed, which we will see a little later.

Side note here: the best practice is to use the __name__ attribute for naming loggers like this: logging.getLogger(__name__). This way, each file…