Check specific file has been modified using python watchdog

Question

i would like to know how to check change of a specific file under a folder. I found that watchdog module could check change for files in folder but i need 1 file only (with fixed name).

Please kindly help on this and thanks.

class MyHandler(FileModifiedEvent):
    def on_modified(self, event):

if __name__ == "__main__":
        integrity_file_path = DATASTORE_DIRECTORY_PATH + '/schedule.xml'
        event_handler = MyHandler()
        observer = Observer()
        observer.schedule(MyHandler(), path=integrity_file_path,recursive=True)
        observer.start()

        try:
            while True:
                time.sleep(5)
        except KeyboardInterrupt:
            observer.stop()
        observer.join()

Answer 1

You can subclass the watchdog.events.PatternMatchingEventHandler event handler and modify it to do whatever you want in the case of an event. You would set the pattern to be the filename that you want to monitor.

However, this one's a bit tricky. Under the covers it's using pathtools.patterns to do its pattern matching. And it's also appending the directory to the pattern being matched. Which means you'll need to pass into the event handler the full path of your file as your filename "pattern" argument. If you don't, the pattern matching will fail and you won't get any event notifications.

Here's an example below:

import sys, os.path, time, logging
from watchdog.observers import Observer
from watchdog.events import PatternMatchingEventHandler


class MyEventHandler(PatternMatchingEventHandler):
    def on_moved(self, event):
        super(MyEventHandler, self).on_moved(event)
        logging.info("File %s was just moved" % event.src_path)

    def on_created(self, event):
        super(MyEventHandler, self).on_created(event)
        logging.info("File %s was just created" % event.src_path)

    def on_deleted(self, event):
        super(MyEventHandler, self).on_deleted(event)
        logging.info("File %s was just deleted" % event.src_path)

    def on_modified(self, event):
        super(MyEventHandler, self).on_modified(event)
        logging.info("File %s was just modified" % event.src_path)

def main(file_path=None):
    logging.basicConfig(level=logging.INFO,
        format='%(asctime)s - %(message)s',
        datefmt='%Y-%m-%d %H:%M:%S')
    watched_dir = os.path.split(file_path)[0]
    print 'watched_dir = {watched_dir}'.format(watched_dir=watched_dir)
    patterns = [file_path]
    print 'patterns = {patterns}'.format(patterns=', '.join(patterns))
    event_handler = MyEventHandler(patterns=patterns)
    observer = Observer()
    observer.schedule(event_handler, watched_dir, recursive=True)
    observer.start()
    try:
        while True:
            time.sleep(1)
    except KeyboardInterrupt:
        observer.stop()
    observer.join()



if __name__ == "__main__":
    if len(sys.argv) > 1:
        path = sys.argv[1]
        main(file_path=path.strip())
    else:
        sys.exit(1)

Executing the watchdog python script (before modifying the file):

(stackoverflow)[root@joeyoung.io stackoverflow]# python watchschedule.py /usr/local/src/stackoverflow/watchdog/schedule.xml
watched_dir = /usr/local/src/stackoverflow/watchdog
patterns = /usr/local/src/stackoverflow/watchdog/schedule.xml

Modifying the schedule.xml file in a separate console:

[root@joeyoung.io watchdog]# echo "I just modified this file" >> schedule.xml

Results after modifying schedule.xml:

(stackoverflow)[root@joeyoung.io stackoverflow]# python watchschedule.py /usr/local/src/stackoverflow/watchdog/schedule.xml
watched_dir = /usr/local/src/stackoverflow/watchdog
patterns = /usr/local/src/stackoverflow/watchdog/schedule.xml
2015-08-31 19:30:31 - File /usr/local/src/stackoverflow/watchdog/schedule.xml was just modified

Answer 2

I would say you can check the modification time for the file according to

How to get file creation & modification date/times in Python?

Define a threshold and compare the current time with the modification time, you may know if the file is updated. This would work if the file is not getting modified super frequently.

But anyway, there's gonna be false alarm if someone opened the file, typed in some garbage then deleted and saved.