Logging in python

Adding logging to your python applications is simple with the standard logging module. The best part about having a standard logging module, is that every application has the ability to send log information in the same way.

In today’s post, I’ll go through a small howto on setting up logging.

Logging levels

Much like any other logging framework, python’s logging framework expects that you’ll send messages out to the logger that belong to a particular class (or level). The levels are as follows:

Getting started

import logging

logging.debug('Debug message')
logging.info('Info message')
logging.warning('Warning message')
logging.error('Error message')
logging.critical('Critical message')

The code above ends up emitting the following text:

WARNING:root:Warning message
ERROR:root:Error message
CRITICAL:root:Critical message

You notice a couple of things here; first we asked for a debug and info message here but we never saw one. Secondly, we see the format of the messages being written:

LEVEL:NAME:MESSAGE

We’re using the root logger.

The default logging level is WARNING. Anything requested below this (like INFO and DEBUG) are not emitted by the logger. We can change this with basicConfig.

logging.basicConfig(level=logging.DEBUG)

Being that DEBUG is the lowest level logger that you can ask for, we should see all of the messages.

Further configuration

To give your logger a little more context for your application, you can control the formatting parameters. The information that you can specify into your log lines is specified here.

For this example, we’ll just have the time and the log line.

logging.basicConfig(format='%(asctime)s %(message)s', level=logging.DEBUG)

We now are presented with the following:

2016-02-06 22:26:27,494 Debug message
2016-02-06 22:26:27,494 Info message
2016-02-06 22:26:27,494 Warning message
2016-02-06 22:26:27,494 Error message
2016-02-06 22:26:27,494 Critical message

There is so much more to look at in this module and you can find it here.