Stop Writing Your Error Messages to stdout

Note#107

notes
Published

2023-07-23

Using print() is easy and convenient, but it prints everything to stdout. It can be the right tool for quick and dirty debugging—everyone does it. However, it’s not without its problems. For instance, what if we want the output to go to a file instead of the screen (for logging purposes)? Also, do we really want to print our error messages to stdout in production?

Using print() with the file parameter

import sys

print("This is an error message.", file=sys.stderr)

Using the sys.stderr object

import sys

sys.stderr.write("This is an error message.\n")

Note that it’s important to include the newline character \n at the end of the message to ensure proper formatting.

Using click.echo()

The Click library allows printing to stderr by passing err=True to click.echo().

import click

click.echo("This is an error message.", err=True)

Logging Error Messages

The logging module from the standard library should be preferred for complex and serious production code.

It solves the problems mentioned above and even more. It also allows for five levels of logging (from critical to debug).

Example

Here’s an example of how to configure a logging handler to write error messages to a file:

import logging

# Create a logger
logger = logging.getLogger('error_logger')
logger.setLevel(logging.ERROR)

# Create a file handler
file_handler = logging.FileHandler('error.log')

# Set the formatter
formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s')
file_handler.setFormatter(formatter)

# Add the handler to the logger
logger.addHandler(file_handler)

# Write an error message to the log file
logger.error("This is an error message.")

This example sets the logging level to ERROR to ensure that only error messages are written to the file. The log format is specified using a formatter, which includes the timestamp, log level, and log message. The logger.error() method is used to write the error message to the log file.

By logging error messages to a file, you can easily track and analyze them, helping to identify and troubleshoot issues more effectively.

References