How do you use Python watchdog?

1 year ago
Noah Thompson
2 minutes

Watchdog is a Python library used to monitor changes in the file system. It can keep track of operations such as creating, modifying, deleting, or moving files or directories, triggering events when these changes occur.

The general steps of using Watchdog are as follows:

  1. Install the Watchdog library: Use the pip command to install the Watchdog library: pip install watchdog.
  2. Import the Watchdog library: Import the Watchdog library in a Python script: import watchdog.
  3. Define an event handling class: Create a class that inherits from watchdog.events.FileSystemEventHandler and override the corresponding methods to handle different events. For instance, override the on_modified method to handle file modification events, and override the on_created method to handle file creation events.
  4. Create observers and handlers: Instantiate a watchdog.observers.Observer object as an observer and associate it with the event handling class defined earlier.
  5. Add an observation path: use the observer’s schedule method to add the file or directory path to be observed.
  6. Start the observer: Launch the observation using the start method of the observer.
  7. Handling events: When changes occur in the file system, the observer will call the corresponding methods in the event handling class to handle the events.

Here is a simple sample code that monitors modification events of files in a specified path.

import time
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler

class MyEventHandler(FileSystemEventHandler):
    def on_modified(self, event):
        if not event.is_directory:
            print(f'File {event.src_path} has been modified')

if __name__ == "__main__":
    event_handler = MyEventHandler()
    observer = Observer()
    observer.schedule(event_handler, path='/path/to/watch', recursive=True)
    observer.start()

    try:
        while True:
            time.sleep(1)
    except KeyboardInterrupt:
        observer.stop()

    observer.join()

In the code above, when a file in the specified path is modified, corresponding information will be outputted.

It is important to note that when using Watchdog, observers should be run in a separate thread to avoid blocking the main thread’s execution.

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