watchdog monitoring file for changes

Question

I have a need to watch a log file for changes. After looking through stackoverflow questions, I see people recommending watchdog. So I’m trying to test, and am not sure where to add the code for when files change:

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

if __name__ == "__main__":
    event_handler = LoggingEventHandler()
    observer = Observer()
    observer.schedule(event_handler, path='.', recursive=False)
    observer.start()
    try:
        while True:
            time.sleep(1)
        else:
            print "got it"
    except KeyboardInterrupt:
        observer.stop()
    observer.join()

Where do I add the "got it" — in the while loop if the files have been added/changed?

Asked By: Cmag

||

Source

Answer 1

Instead of LoggingEventHandler define your handler:

#!/usr/bin/python
import time
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler


class MyHandler(FileSystemEventHandler):
    def on_modified(self, event):
        print(f'event type: {event.event_type}  path : {event.src_path}')


if __name__ == "__main__":
    event_handler = MyHandler()
    observer = Observer()
    observer.schedule(event_handler, path='/data/', recursive=False)
    observer.start()

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

on_modified is called when a file or directory is modified.

Answered By: alecxe

Answer 2

Here’s a snippet to prevent it running twice as others have commented in @alecxe answer:

from datetime import datetime, timedelta

class MyHandler(FileSystemEventHandler):
    def __init__(self):
        self.last_modified = datetime.now()

    def on_modified(self, event):
        if datetime.now() - self.last_modified < timedelta(seconds=1):
            return
        else:
            self.last_modified = datetime.now()
        print(f'Event type: {event.event_type}  path : {event.src_path}')
        print(event.is_directory) # This attribute is also available

Answered By: run_the_race

Answer 3

Instead of datetime, you may go with the src_path check logic since if the logic after the checking more than 1-second datetime logic will fail.

class EventHandler(FileSystemEventHandler):
    def __init__(self):
        self.src_path = ''

    def on_modified(self, event):
        if self.src_path == event.src_path:
            return
        else:
            self.src_path = event.src_path
        logger.info(f"{event.event_type} occured on file {self.src_path}")
        #your long processing logics goes here.

Answered By: Basil Jose

Answer 4

For others that came across this question and want the answer for: "how to watch a specific file", also asked by @Cmag, this is a quick way to watch specific files. You set the specific files as regexes and use

directory_to_watch = './'
event_handler = RegexMatchingEventHandler(regexes=['.*/config.json'])
observer = Observer()
observer.schedule(event_handler, directory_to_watch, recursive=False)
observer.start()
try:
    while True:
        time.sleep(1)
finally:
    observer.stop()
    observer.join()

Answered By: Ianau Andrei

watchdog monitoring file for changes

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