Many times a file is needed to be processed at the time of its creation or its modification. This can be done by following changes in a particular directory. There are many ways in python to follow changes made in a directory. One such way is to use the watchdog module. As the name suggests this module observes the given directory and can notify if a file is created or changed.
Modules needed
- Watchdog To install watchdog run this command in the terminal.
pip install watchdog
- Logging It comes built-in with python, so there is no need to externally install it.
Now let’s dive into the code that will log all the changes registered. This code will log changes registered only in the current directory.
# import the modules import sys
import time
import logging
from watchdog.observers import Observer
from watchdog.events import LoggingEventHandler
if __name__ = = "__main__":
# Set the format for logging info
logging.basicConfig(level = logging.INFO,
format = '%(asctime)s - %(message)s' ,
datefmt = '%Y-%m-%d %H:%M:%S' )
# Set format for displaying path
path = sys.argv[ 1 ] if len (sys.argv) > 1 else '.'
# Initialize logging event handler
event_handler = LoggingEventHandler()
# Initialize Observer
observer = Observer()
observer.schedule(event_handler, path, recursive = True )
# Start the observer
observer.start()
try :
while True :
# Set the thread sleep time
time.sleep( 1 )
except KeyboardInterrupt:
observer.stop()
observer.join()
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Output:
# import time module, Observer, FileSystemEventHandler import time
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
class OnMyWatch:
# Set the directory on watch
watchDirectory = " / give / the / address / of / directory"
def __init__( self ):
self .observer = Observer()
def run( self ):
event_handler = Handler()
self .observer.schedule(event_handler, self .watchDirectory, recursive = True )
self .observer.start()
try :
while True :
time.sleep( 5 )
except :
self .observer.stop()
print ("Observer Stopped")
self .observer.join()
class Handler(FileSystemEventHandler):
@staticmethod
def on_any_event(event):
if event.is_directory:
return None
elif event.event_type = = 'created' :
# Event is created, you can process it now
print ("Watchdog received created event - % s." % event.src_path)
elif event.event_type = = 'modified' :
# Event is modified, you can process it now
print ("Watchdog received modified event - % s." % event.src_path)
if __name__ = = '__main__' :
watch = OnMyWatch()
watch.run()
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Output:
Deciphering the code
Observer
The Observer is the class that watches for any file system change and then dispatches the event to the event handler. It monitors the file system and look for any changes.
Event Handler
The event handler is an object that will be notified when something happens to the file system. In general a script is written to watch over any type of new files created or modified like jpg, xml etc. For example, in the code below the PatternMatchingEventHandler inherits from the FileSystemEventHandler class and is used to do just that. Some useful methods of this class are:
- on_any_event: will be executed for any event.
- on_created: Executed when a file or a directory is created.
- on_modified: Executed when a file is modified or a directory renamed.
- on_deleted: Executed when a file or directory is deleted.
- on_moved: Executed when a file or directory is moved.
Each one of those methods receives the event object as first parameter, and the event object has 3 attributes:
- event_type: modified/created/moved/deleted
- is_directory: True/False
- src_path: path/to/observe/file
The below script is used to observe only .csv files using the PatternMAtchingEventHandler. You can further extend the patterns list if you want to observe more than one type of file.
import watchdog.events
import watchdog.observers
import time
class Handler(watchdog.events.PatternMatchingEventHandler):
def __init__( self ):
# Set the patterns for PatternMatchingEventHandler
watchdog.events.PatternMatchingEventHandler.__init__( self , patterns = [ '*.csv' ],
ignore_directories = True , case_sensitive = False )
def on_created( self , event):
print ("Watchdog received created event - % s." % event.src_path)
# Event is created, you can process it now
def on_modified( self , event):
print ("Watchdog received modified event - % s." % event.src_path)
# Event is modified, you can process it now
if __name__ = = "__main__":
src_path = r"C:\Users\GeeksforGeeks\PycharmProjects\requests hotel"
event_handler = Handler()
observer = watchdog.observers.Observer()
observer.schedule(event_handler, path = src_path, recursive = True )
observer.start()
try :
while True :
time.sleep( 1 )
except KeyboardInterrupt:
observer.stop()
observer.join()
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Output: