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Monitor big text file for change and show what was added

I try to monitor text log file for changes and want to see lines that was added
I try with watchdog it seems to work with some manually created/edited files for testing, but my log file (in the same directory) isn't detected as "changed", but it was changed. It's probably because this file is already open (maybe in a specific mode). If I close the app that uses this log file and change it manually then watchdog works ok.
How do I check if the file was changed and if the changes were written to
the console?
#!/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='C:\gory\parcienaszklo\logs', recursive=False)
observer.start()
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
observer.stop()
observer.join()

Detect the changes in a file and write them in a file

I produced a script that detects the changes on files that are located in a specific directory. I'm trying to write all these changes to a changes.txt file. For this purpose I'm using the sys.stdout = open('changes.txt','w') instruction.
The problem is that whenever I run the script and change a file in the directory and save it, an empty file called changes.txt is created. This file is never written!
#!/usr/bin/python
import time
import sys
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
sys.stdout = open('changes.txt','w')
class MyHandler(FileSystemEventHandler):
def on_modified(self, event):
print "something happened!"
if __name__ == "__main__":
event_handler = MyHandler()
observer = Observer()
observer.schedule(event_handler, path='.', recursive=False)
observer.start()
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
observer.stop()

I'd recommend something like
#!/usr/bin/python
import time
import sys
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
class MyHandler(FileSystemEventHandler):
def __init__(self, f):
self.f = f
def on_modified(self, event):
self.f.write("something happened!\n")
self.f.flush()
if __name__ == "__main__":
with open('changes.txt','w') as f:
event_handler = MyHandler(f)
observer = Observer()
observer.schedule(event_handler, path='.', recursive=False)
observer.start()
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
observer.stop()
as you can see, the control over where your outputwill be written to has been handed to the caller (the one instanciating MyHandler) instead of the callee (on_modified).
This means you can also do
event_handler = MyHandler(sys.stdout)
and see the output instead of the output being put into the file.
An additional benefit: using a context manager you can be sure the file is closed properly, even if errors occurr.

Getting the filename using python Watchdog

I am trying to get the name of a file that changes periodically.
I am using watchdog to do this.
import time
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
timestr = time.strftime("%Y.%m.%d-%H.%M.%S")
class MyHandler(FileSystemEventHandler):
def on_modified(self, event):
change_log = open('change_log_' + timestr + '.txt', 'aw')
change_log.write('Time the file changed: ' + timestr + '\n')
change_log.close()
if __name__ == "__main__":
event_handler = MyHandler()
observer = Observer()
observer.schedule(event_handler, path='.', recursive=False)
observer.start()
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
observer.stop()
observer.join()
For some reason this prints out about 62 lines in the "change_log" file. This is not very useful.
What I would like to do is to print the name of the file that changed, or store it in a variable to pass to my other module.

In your example, if you need a file name, it is necessary to replace 'change_log_' with event.src_path. See the official code for more details.
You can also see the use of event.src_path in this answer as I used it in the printout.

It looks like the event object that is sent to your handler includes the information that you seek:
http://pythonhosted.org/watchdog/api.html#watchdog.events.FileSystemEvent
Use the src_path property of the event object that's passed into your FileSystemEvent subclass handler method to get the filename.

Stop monitoring a file with watchdog

I have this small script to monitoring with watchdog one single file (test.txt).
Till now I got a screen message each time the file is modified but I need just the get the notification for the first time, it's mean to stop monitoring, is there any way I could tell watchdog to stop it?
Here is my code:
#!/usr/bin/python
import time
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
file_to_scan = "test.txt"
class MyHandler(FileSystemEventHandler):
def on_modified(self, event):
if file_to_scan in event.src_path:
print "Got it!", event.src_path
#### I want to stop here the monitoring
def on_created(self, event):
pass
if __name__ == "__main__":
event_handler = MyHandler()
observer = Observer()
observer.schedule(event_handler, path ="." , recursive=False)
observer.start()
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
observer.stop()
observer.join()

How to match only particular events with Python watchdog

I'm intending to use Python watchdog to handle a directory where files are written to,
and I'm only interested in image files, trouble is I dont quite grok the code at this page.
This is my attempt:
from watchdog.observers import Observer
from watchdog.events import PatternMatchingEventHandler
class Beat(PatternMatchingEventHandler):
def on_create(self,event):
print event.src_path
if __name__ == "__main__":
patt = ['\w+[.]jpeg']
event_handler = Beat(patterns=patt,ignore_directories=True,)
observer = Observer()
path = "./"
observer.schedule(event_handler, path, recursive=True)
observer.start()
I'm trying to use the pattern matching class, but I'm getting nothing. How is it supposed to be used?

Based on the source code, fnmatch is being used under the hood. fnmatch can only do UNIX glob-style pattern matching. Which means you may have better luck with *.jpg than \w+[.]jpeg

You can actually use the RegexMatchingEventHandler instead of PatternMatchingEventHandler to accomplish exactly what you want to do:
from watchdog.observers import Observer
from watchdog.events import RegexMatchingEventHandler
class ExampleHandler(RegexMatchingEventHandler):
def on_create(self, event):
print(event.src_path)
if __name__ == "__main__":
pattern = '\w+\.jpeg'
event_handler = ExampleHandler(regexes=[pattern], ignore_directories=True)
observer = Observer()
path = "./"
observer.schedule(event_handler, path, recursive=True)
observer.start()
import time
try:
while True:
time.sleep(1)
except KeyboardInterrupt:
observer.stop()
observer.join()