Watchdog
The Watchdog Extension includes the
WatchdogManager, enabling applications to easily monitor, and react to, changes in filesystem paths based on the filesystem events monitoring library Watchdog.On application startup, the Watchdog Observer is automatically started and then upon application close, the observer thread is properly stopped and joined with the parent process before exit.
API References:
- Watchdog
Cement 3.0.8+:
pip install cement[watchdog]Applications using Cement <3.0.8 should continue to include
watchdog in their dependencies.- Unix/Linux
- macOS
- Windows
This extension does not support any application level configuration settings.
This extension honors the following application meta options:
Option | Description |
watchdog_paths | A list of tuples that are passed directly as arguments to WatchdogManager.add() (a shortcut equivalent to app.watchdog.add(). |
This extension defines the following hooks:
Run first when
App.watchdog.start() is called. The application object is passed as an argument. Nothing is expected in return.Run last when
App.watchdog.start() is called. The application object is passed as an argument. Nothing is expected in return.Run first when
App.watchdog.stop() is called. The application object is passed as an argument. Nothing is expected in return.Run last when
App.watchdog.stop() is called. The application object is passed as an argument. Nothing is expected in return.Run first when
App.watchdog.join() is called. The application object is passed as an argument. Nothing is expected in return.Run last when
App.watchdog.join() is called. The application object is passed as an argument. Nothing is expected in return.The following example uses the default
WatchdogEventHandler that by default only logs all events to debug:Example: Using Watchdog Extension
from time import sleep
from cement import App, CaughtSignal
from cement.ext.ext_watchdog import WatchdogEventHandler
class MyApp(App):
class Meta:
label = 'myapp'
extensions = ['watchdog']
watchdog_paths = [
('./tmp/', WatchdogEventHandler),
]
with MyApp() as app:
app.run()
try:
while True:
sleep(1)
except CaughtSignal as e:
print(e)
In the above example, nothing is printed to console. However you will see something like the following via debug logging:
$ python myapp.py --debug 2>&1 | grep -i watchdog
cement.core.extension : loading the 'cement.ext.ext_watchdog' framework extension
cement.core.hook : defining hook 'watchdog_pre_start'
cement.core.hook : defining hook 'watchdog_post_start'
cement.core.hook : defining hook 'watchdog_pre_stop'
cement.core.hook : defining hook 'watchdog_post_stop'
cement.core.hook : defining hook 'watchdog_pre_join'
cement.core.hook : defining hook 'watchdog_post_join'
cement.core.hook : registering hook 'watchdog_extend_app' from cement.ext.ext_watchdog into hooks['post_setup']
cement.core.hook : registering hook 'watchdog_add_paths' from cement.ext.ext_watchdog into hooks['post_setup']
cement.core.hook : registering hook 'watchdog_start' from cement.ext.ext_watchdog into hooks['pre_run']
cement.core.hook : registering hook 'watchdog_cleanup' from cement.ext.ext_watchdog into hooks['pre_close']
cement.core.hook : running hook 'post_setup' (<function watchdog_extend_app at 0x103c991e0>) from cement.ext.ext_watchdog
cement.core.foundation : extending appication with '.watchdog' (<cement.ext.ext_watchdog.WatchdogManager object at 0x103f83ef0>)
cement.core.hook : running hook 'post_setup' (<function watchdog_add_paths at 0x103ddd6a8>) from cement.ext.ext_watchdog
cement.ext.ext_watchdog : adding path /path/to/tmp with event handler <class 'cement.ext.ext_watchdog.WatchdogEventHandler'>
cement.core.hook : running hook 'pre_run' (<function watchdog_start at 0x103ddd598>) from cement.ext.ext_watchdog
cement.ext.ext_watchdog : starting watchdog observer
myapp : Watchdog Event: <FileDeletedEvent: src_path='/path/to/tmp/test2'>
myapp : Watchdog Event: <FileDeletedEvent: src_path='/path/to/tmp/test4'>
myapp : Watchdog Event: <FileDeletedEvent: src_path='/path/to/tmp/test3'>
myapp : Watchdog Event: <FileDeletedEvent: src_path='/path/to/tmp/dir1/test'>
myapp : Watchdog Event: <FileDeletedEvent: src_path='/path/to/tmp/test'>
myapp : Watchdog Event: <DirDeletedEvent: src_path='/path/to/tmp/dir1'>
myapp : Watchdog Event: <DirModifiedEvent: src_path='/path/to/tmp'>
myapp : Watchdog Event: <DirModifiedEvent: src_path='/path/to/tmp'>
myapp : Watchdog Event: <DirCreatedEvent: src_path='/path/to/tmp/dir1'>
myapp : Watchdog Event: <FileCreatedEvent: src_path='/path/to/tmp/dir1/test.file'>
myapp : Watchdog Event: <DirModifiedEvent: src_path='/path/to/tmp/dir1'>
cement.core.hook : running hook 'pre_close' (<function watchdog_cleanup at 0x10e930620>) from cement.ext.ext_watchdog
cement.ext.ext_watchdog : stopping watchdog observer
cement.ext.ext_watchdog : joining watchdog observer
cement.core.foundation : closing the myapp application
To expand on the above example, we can add our own event handlers:
Example: Adding Watchdog Event Handlers
cli
myapp.py
from time import sleep
from cement import App, CaughtSignal
from cement.ext.ext_watchdog import WatchdogEventHandler
class MyEventHandler(WatchdogEventHandler):
def on_any_event(self, event):
# do something with the ``event`` object
print("The modified path was: %s" % event.src_path)
class MyApp(App):
class Meta:
label = 'myapp'
extensions = ['watchdog']
watchdog_paths = [
('./tmp/', MyEventHandler),
]
with MyApp() as app:
app.run()
try:
while True:
sleep(1)
except CaughtSignal as e:
print(e)
$ python myapp.py
The modified path was: /path/to/tmp/test.file
Note that the
WatchdogEventHandler could be replaced with any other event handler classe (i.e. those available from watchdog directly). However to play nicely with Cement, we sub-class them first in order to pass in our application object.Example: Creating a Watchdog Event Handler
from watchdog.events import FileSystemEventHandler
class MyEventHandler(FileSystemEventHandler):
def __init__(self, app, *args, **kw):
super(MyEventHandler, self).__init__(*args, **kw)
self.app = app
Last modified 7mo ago