Logging in Python¶

The Basics:¶

The Logging module is a built-in module, so installation is not necessary. I only need to import it.

import logging

There are several elements in the logging, but the most important are: * Logging levels. * Handler. * Formatter.

Logging Levels¶

Logging levels will allow me to log more specific things, such as; debugging statements, information, or reports errors.

Levels	Descriptions
DEBUG	Detailed information, mostly for diagnostics.
INFO	Mostly to confirm that something is working.
WARNING	Something happens that can create problems in the future.
ERROR	A serious problem, the software cannot perform the action.
CRITICAL	Serious Error, unable to continue.

Example of a basic logging¶

This example will show the simple logging configuration. There is no configuration for a handler or a formatter. However, the implementation will allow me to decide whether I want to log the information in a file and in what format I want the information.

Just with the logging level, the default output will be the console.¶

logging_001

Adding a destination file¶

logging_002

Changing the format of the output¶

logging_003

In the above example, I configure the logs to display the time and a message, But these are not the only attributes I can use. python documentation provides an extensive list of LogRecord attributes here:

Logging documentation

The complete code of the basic example will be:

logging_004

Advanced Logging¶

I have just one logger in the following example -a good option if I deal with one script at a time. But for a more complex app, I will need more loggers and probably more output. To achieve a more functional logger, I can make use of the elements mentioned previously * Logging levels. * Handler. * Formatter.

The following code can be duplicated in each script to have a logger in each one of them

Creating a logger for a specific script¶

I start by creating a variable: logging_006 logging_005

The argument name is a deeper topic that I won't cover here. but a bad explanation or rather a not accurate one will say; "this will help the lower to know in which module and function it is been call".

Logging Levels¶

To add the logging level to the logger, I use the function setLevel(). logging_007

Handler¶

In this case refer to which output I will use, the console or a document.

logging_008 I created a file handler, but it is not linked to the logger yet, I need to add it.

logging_009

Be aware that I haven't changed the format of the output, I just define what will be the output for the logger. To add a stream handler or an output to the console, I can use StreamHandler().

logging_010

Formatter¶

Now with the logger added I can think in the format I want. To modify the format I can use setFormatter().

logging_011

The extra argument datefmt allows me to modify how the time is displayed. Similar to Handler, I have to register it with the logger. setFormatter() is used to add the format to the logger. logging_012

Now, all together: logging_013

Notes:¶

When using try/except blocks is a good idea to log the traceback when the action fails by using the function .exception() with the logger.