python watchdog runs more than once

Question

I am trying to learn python-watchdog, but I am sort of confused why the job I set up runs more than once. So, here is my set up:

#handler.py
import os
from watchdog.events import FileSystemEventHandler
from actions import run_something

def getext(filename):
    return os.path.splitext(filename)[-1].lower()

class ChangeHandler(FileSystemEventHandler):

    def on_any_event(self, event):

        if event.is_directory:
            return
        if getext(event.src_path) == '.done':
            run_something()
        else: 
            print "event not directory.. exiting..."
            pass

the observer is set up like so:

#observer.py
import os
import time
from watchdog.observers import Observer
from handler import ChangeHandler

BASEDIR = "/path/to/some/directory/bin"

def main():

    while 1:

        event_handler = ChangeHandler()
        observer = Observer()
        observer.schedule(event_handler, BASEDIR, recursive=True)
        observer.start()
        try:
            while True:
                time.sleep(1)
        except KeyboardInterrupt:
            observer.stop()
        observer.join()

 if __name__ == '__main__':
    main()

and finally, the actions like so:

#actions.py
import os
import subprocess

def run_something():
    output = subprocess.check_output(['./run.sh'])
    print output
    return None

..where ./run.sh is just a shell script I would like to run when a file with an extension .done is found on /path/to/some/directory/bin

#run.sh
#!/bin/bash
echo "Job Start: $(date)"
rm -rf /path/to/some/directory/bin/job.done # remove the .done file
echo "Job Done: $(date)"

However, when I issue a python observer.py and then do a touch job.done on /path/to/some/directory/bin, I see that my shell script ./run.sh runs three times and not one..

I am confused why this runs thrice and not just once (I do delete the job.done file on my bash script)

Answer 1

To debug watchdog scripts, it is useful to print what watchdog is seeing as events. One file edit or CLI command, such as touch, can result in multiple watchdog events. For example, if you insert a print statement:

class ChangeHandler(FileSystemEventHandler):

    def on_any_event(self, event):
        print(event)

to log every event, running

% touch job.done

generates

2014-12-24 13:11:02 - <FileCreatedEvent: src_path='/home/unutbu/tmp/job.done'>
2014-12-24 13:11:02 - <DirModifiedEvent: src_path='/home/unutbu/tmp'>
2014-12-24 13:11:02 - <FileModifiedEvent: src_path='/home/unutbu/tmp/job.done'>

---

Above there were two events with src_path ending in job.done. Thus,

    if getext(event.src_path) == '.done':
        run_something()

runs twice because there is a FileCreatedEvent and a FileModifiedEvent. You might be better off only monitoring FileModifiedEvents.

Answer 2

I Made a fix for watchdog:

import watchdog.events
import watchdog.observers
import time

osb = None

class Handler(watchdog.events.PatternMatchingEventHandler):
    def on_any_event(self, event):
        global osb
        osb = None
        print(f"Watchdog received {event} event - {event.src_path}.")
 
    def on_modified(self, event):
        global osb
        if not osb == event.src_path:
            #Code goes here
        osb = event.src_path
 
 
if __name__ == "__main__":
    src_path = r"C:\\Users\\Administrator\\Desktop\\"
    event_handler = Handler()
    observer = watchdog.observers.Observer()
    observer.schedule(event_handler, path=src_path, recursive=True)
    observer.start()
    try:
        while True:
            time.sleep(0)
    except KeyboardInterrupt:
        observer.stop()
    observer.join()

No I will not explain, sorry(forgot how it works and don't have time to find out).