How Can I Efficiently Monitor Log File Changes in Python Without Polling?

Monitoring File Changes in Python

This article addresses the challenge of monitoring a log file for changes and reading the updated data for processing. The original question expressed the desire to find a non-polling solution, potentially using PyWin32.

For this purpose, the Python library Watchdog offers a promising solution. Watchdog is designed to monitor file system events across multiple platforms. It provides an API that allows developers to define custom event handlers to perform specific actions when files are modified or created.

Using Watchdog, one can set up a simple event handler to watch a particular log file and read its contents upon any change. Here's an example:

import watchdog.observers as observers
import watchdog.events as events

class FileEventHandler(events.FileSystemEventHandler):
    def on_modified(self, path, event):
        with open(path, 'r') as f:
            data = f.read()
            # Process the new data here

# Path to the log file
log_path = '/path/to/log.txt'

# Create the file handler
handler = FileEventHandler()

# Create the observer and schedule the log file for monitoring
observer = observers.Observer()
observer.schedule(handler, log_path, recursive=False)

# Start the observer
observer.start()

# Blocking code to keep the observer running
observer.join()

With this setup, any modifications to the log file will trigger the on_modified method, which in turn reads and processes the new data. By providing a reliable and efficient way to monitor file changes, Watchdog alleviates the need for polling and offers a practical solution for this specific requirement.

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