Python watchdog polling observer

Edwin 168 Published: 10/05/2024

Python watchdog polling observer

I'd be happy to provide information on a Python watchdog and its related concepts.

Python Watchdog is an open-source project that provides a cross-platform, high-performance monitoring and control tool for systems, applications, and devices. It's built with the following principles in mind:

Simple: Easy-to-use APIs make it straightforward to integrate Watchdog into your existing infrastructure.

Reliable: High-performance event handling and processing ensure timely detection of system changes or malfunctions.

Now, let's talk about polling observers! In Python Watchdog, an observer is a class that inherits from watchdog.observers.Observer and provides custom logic for monitoring specific file systems, directories, or devices. The polling observer (also known as FileSystemObserver) is a type of observer that periodically checks a directory or file system for changes.

Here's how it works:

Initialization: You create an instance of the FilesystemObserver class and pass in the path to the directory or file system you want to monitor. Periodic polling: The observer uses Python's built-in os.path module to check for changes at regular intervals (configurable by the interval parameter). This can include: File creation, modification, or deletion Directory creation, modification, or deletion Changes to file system metadata (e.g., timestamps)

Event handling: When a change is detected, the observer triggers an event, which can be handled by one or more Handler instances.

Example of using a polling observer with Watchdog:

import watchdog.observers
Create a FileSystemObserver instance

observer = watchdog.observers.FileSystemObserver('/path/to/monitor')

Define an event handler (e.g., print the changed files)

def on_modified(event):


if event.is_directory:


print(f"Directory {event.src_path} has been modified.")


else:


print(f"File {event.src_path} has been modified.")

Register the event handler with the observer

observer.addEventListener(on_modified, event_type=watchdog.events.MODIFY)

Start the observer (optional: start=True starts the observer immediately)

observer.start()

In this example:

We create a FileSystemObserver instance for the /path/to/monitor directory. We define an on_modified function that will be called whenever a file or directory within the monitored path is modified. This event handler simply prints messages to indicate the changes. We register our event handler with the observer using addEventListener. Finally, we start the observer (optional: set start=True to run it immediately).

In summary, Python Watchdog's polling observer provides a robust mechanism for monitoring file systems and detecting changes at regular intervals. Its high-performance design makes it suitable for a wide range of applications, from simple system monitoring to complex device control.

Python watchdog timer example

I'm happy to provide a Python example for a watchdog timer! However, please note that I'll be responding in English only this time.

A watchdog timer is a simple, yet effective way to detect and recover from software crashes or hangs. In Python, we can implement a watchdog timer using the threading and time modules. Here's an example:

import threading

import time


class Watchdog:


def init(self):


self.stop_event = threading.Event()


self.timer = threading.Timer(5.0, self.stop_timer)


self.timer.setDaemon(True)


def start(self):


self.timer.start()


def stop_timer(self):


print("Timer stopped!")


self.stop_event.set()


def reset(self):


if not self.timer.is_alive():


self.timer = threading.Timer(5.0, self.stop_timer)


self.timer.setDaemon(True)


self.timer.start()


def task():


while True:

Your code here

print("Running...")


time.sleep(2)


if name == "main":


watchdog = Watchdog()


thread = threading.Thread(target=task)


thread.start()


watchdog.start()


try:


while not watchdog.stop_event.is_set():


pass


except KeyboardInterrupt:


print("Caught KeyboardInterrupt!")


finally:


if watchdog.timer.is_alive():


watchdog.timer.cancel()


watchdog.reset()

In this example, we create a Watchdog class that uses a threading.Timer to trigger the stop_timer method after 5 seconds. The start method starts the timer, and the reset method restarts the timer if it's not already running.

We also define a task function that runs indefinitely and sleeps for 2 seconds between iterations. This represents the "heavy" operation you want to watchdog.

In the main script, we create an instance of the Watchdog class and start a thread running the task function. We then call the start method on the watchdog object to start the timer.

The main loop waits for the stop_event event set by the stop_timer method to become True, indicating that the timer has stopped. When this happens, we catch the KeyboardInterrupt exception (if one is raised) and cancel the timer using timer.cancel() before resetting the watchdog with watchdog.reset().

This example demonstrates a basic watchdog timer implementation in Python. You can adapt it to your specific needs by modifying the task function and adjusting the timer duration as required.

Now, if you'll excuse me, I have some important coding tasks to attend to...

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