Logging to a File in Python

General Discussions
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1

How can I use the python log to file functionality with the logging module?

Every time I try to use it, it just prints out the message. How can I properly write logs to a file using the logging module in Python?

2

Getting started with file logging is actually pretty straightforward. You can configure basic logging using the basicConfig() function. Here’s a simple example to help you log messages to a file:

import logging

# Configure logging to write to a file
logging.basicConfig(
    filename='app.log',  
    level=logging.INFO,  
    format='%(asctime)s - %(levelname)s - %(message)s'  
)

# Log some messages
logging.info('This is an info message')  
logging.error('This is an error message')

In this setup, the basicConfig() method takes care of everything—specifying the file (app.log), the logging level (INFO), and the log format. Once you run this, you’ll see the logs neatly written to app.log. It’s perfect for simple use cases involving python log to file.

3

That’s a great starting point! However, for more advanced control over your logging, you can use a FileHandler. This gives you more flexibility in customizing your log handling behavior. Here’s an example:

import logging

# Create a logger instance
logger = logging.getLogger()  

# Set the logging level
logger.setLevel(logging.INFO)  

# Create a FileHandler
file_handler = logging.FileHandler('app.log')  

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

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

# Log some messages
logger.info('This is an info message')  
logger.error('This is an error message')

With this setup, the FileHandler writes logs to app.log, and you have full control over the format and behavior. This is a great way to enhance your python log to file functionality when basicConfig() feels too limited.

4

Building on Ian’s example, if you’re dealing with large logs, managing file sizes becomes important. You don’t want a single log file to grow endlessly. That’s where the RotatingFileHandler comes in handy:

import logging  
from logging.handlers import RotatingFileHandler  

# Create a logger
logger = logging.getLogger()  

# Set the logging level
logger.setLevel(logging.INFO)  

# Set up a RotatingFileHandler
handler = RotatingFileHandler('app.log', maxBytes=2000, backupCount=5)  

# Format the logs
formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s')  
handler.setFormatter(formatter)  

# Attach the handler to the logger
logger.addHandler(handler)  

# Log some messages
logger.info('This is an info message')  
logger.error('This is an error message')

This setup creates a RotatingFileHandler that limits each log file to 2000 bytes and keeps up to 5 backup files. It’s super useful when you need to maintain python log to file functionality efficiently without bloating your storage.