Code for How to Create a Watchdog in Python Tutorial

config.py

# Application configuration File
################################

# Directory To Watch, If not specified, the following value will be considered explicitly.
WATCH_DIRECTORY = "C:\\SCRIPTS"

# Delay Between Watch Cycles In Seconds
WATCH_DELAY = 1

# Check The WATCH_DIRECTORY and its children
WATCH_RECURSIVELY = False

# whether to watch for directory events
DO_WATCH_DIRECTORIES = True

# Patterns of the files to watch
WATCH_PATTERN = '.txt,.trc,.log'

LOG_FILES_EXTENSIONS = ('.txt', '.log', '.trc')

# Patterns for observations
EXCEPTION_PATTERN = ['EXCEPTION', 'FATAL', 'ERROR']

checker.py

import datetime
from pygtail import Pygtail

# Loading the package called re from the RegEx Module in order to work with Regular Expressions
import re


class FileChecker:
    def __init__(self, exceptionPattern):
        self.exceptionPattern = exceptionPattern

    def checkForException(self, event, path):
        # Get current date and time according to the specified format.
        now = (datetime.datetime.now()).strftime("%Y-%m-%d %H:%M:%S")
        # Read the lines of the file (specified in the path) that have not been read yet
        # Meaning by that it will start from the point where it was last stopped.
        for num, line in enumerate(Pygtail(path), 1):
            # Remove leading and trailing whitespaces including newlines.
            line = line.strip()
            # Return all non-overlapping matches of the values specified in the Exception Pattern.
            # The line is scanned from left to right and matches are returned in the oder found.
            if line and any(re.findall('|'.join(self.exceptionPattern), line, flags=re.I | re.X)):
                # Observation Detected
                type = 'observation'
                msg = f"{now} -- {event.event_type} -- File: {path} -- Observation: {line}"
                yield type, msg
            elif line:
                # No Observation Detected
                type = 'msg'
                msg = f"{now} -- {event.event_type} -- File: {path}"
                yield type, msg

controller.py

# The Observer watches for any file change and then dispatches the respective events to an event handler.
from watchdog.observers import Observer
# The event handler will be notified when an event occurs.
from watchdog.events import FileSystemEventHandler
import time
import config
import os
from checker import FileChecker
import datetime
from colorama import Fore, Style, init

init()

GREEN = Fore.GREEN
BLUE = Fore.BLUE
RED = Fore.RED
YELLOW = Fore.YELLOW

event2color = {
    "created": GREEN,
    "modified": BLUE,
    "deleted": RED,
    "moved": YELLOW,
}


def print_with_color(s, color=Fore.WHITE, brightness=Style.NORMAL, **kwargs):
    """Utility function wrapping the regular `print()` function 
    but with colors and brightness"""
    print(f"{brightness}{color}{s}{Style.RESET_ALL}", **kwargs)


# Class that inherits from FileSystemEventHandler for handling the events sent by the Observer
class LogHandler(FileSystemEventHandler):

    def __init__(self, watchPattern, exceptionPattern, doWatchDirectories):
        self.watchPattern = watchPattern
        self.exceptionPattern = exceptionPattern
        self.doWatchDirectories = doWatchDirectories
        # Instantiate the checker
        self.fc = FileChecker(self.exceptionPattern)

    def on_any_event(self, event):
        now = (datetime.datetime.now()).strftime("%Y-%m-%d %H:%M:%S")
        # print("event happened:", event)
        # To Observe files only not directories
        if not event.is_directory:
            # To cater for the on_move event
            path = event.src_path
            if hasattr(event, 'dest_path'):
                path = event.dest_path
            # Ensure that the file extension is among the pre-defined ones.
            if path.endswith(self.watchPattern):
                msg = f"{now} -- {event.event_type} -- File: {path}"
                if event.event_type in ('modified', 'created', 'moved'):
                    # check for exceptions in log files
                    if path.endswith(config.LOG_FILES_EXTENSIONS):
                        for type, msg in self.fc.checkForException(event=event, path=path):
                            print_with_color(
                                msg, color=event2color[event.event_type], brightness=Style.BRIGHT)
                    else:
                        print_with_color(
                            msg, color=event2color[event.event_type])
                else:
                    print_with_color(msg, color=event2color[event.event_type])
        elif self.doWatchDirectories:
            msg = f"{now} -- {event.event_type} -- Folder: {event.src_path}"
            print_with_color(msg, color=event2color[event.event_type])

    def on_modified(self, event):
        pass

    def on_deleted(self, event):
        pass

    def on_created(self, event):
        pass

    def on_moved(self, event):
        pass


class LogWatcher:
    # Initialize the observer
    observer = None
    # Initialize the stop signal variable
    stop_signal = 0

    # The observer is the class that watches for any file system change and then dispatches the event to the event handler.
    def __init__(self, watchDirectory, watchDelay, watchRecursively, watchPattern, doWatchDirectories, exceptionPattern):
        # Initialize variables in relation
        self.watchDirectory = watchDirectory
        self.watchDelay = watchDelay
        self.watchRecursively = watchRecursively
        self.watchPattern = watchPattern
        self.doWatchDirectories = doWatchDirectories
        self.exceptionPattern = exceptionPattern

        # Create an instance of watchdog.observer
        self.observer = Observer()
        # The event handler is an object that will be notified when something happens to the file system.
        self.event_handler = LogHandler(
            watchPattern, exceptionPattern, self.doWatchDirectories)

    def schedule(self):
        print("Observer Scheduled:", self.observer.name)
        # Call the schedule function via the Observer instance attaching the event
        self.observer.schedule(
            self.event_handler, self.watchDirectory, recursive=self.watchRecursively)

    def start(self):
        print("Observer Started:", self.observer.name)
        self.schedule()
        # Start the observer thread and wait for it to generate events
        now = (datetime.datetime.now()).strftime("%Y-%m-%d %H:%M:%S")
        msg = f"Observer: {self.observer.name} - Started On: {now}"
        print(msg)

        msg = (
            f"Watching {'Recursively' if self.watchRecursively else 'Non-Recursively'}: {self.watchPattern}"
            f" -- Folder: {self.watchDirectory} -- Every: {self.watchDelay}(sec) -- For Patterns: {self.exceptionPattern}"
        )
        print(msg)
        self.observer.start()

    def run(self):
        print("Observer is running:", self.observer.name)
        self.start()
        try:
            while True:
                time.sleep(self.watchDelay)

                if self.stop_signal == 1:
                    print(
                        f"Observer stopped: {self.observer.name}  stop signal:{self.stop_signal}")
                    self.stop()
                    break
        except:
            self.stop()
        self.observer.join()

    def stop(self):
        print("Observer Stopped:", self.observer.name)

        now = (datetime.datetime.now()).strftime("%Y-%m-%d %H:%M:%S")
        msg = f"Observer: {self.observer.name} - Stopped On: {now}"
        print(msg)
        self.observer.stop()
        self.observer.join()

    def info(self):
        info = {
            'observerName': self.observer.name,
            'watchDirectory': self.watchDirectory,
            'watchDelay': self.watchDelay,
            'watchRecursively': self.watchRecursively,
            'watchPattern': self.watchPattern,
        }
        return info


def is_dir_path(path):
    """Utility function to check whether a path is an actual directory"""
    if os.path.isdir(path):
        return path
    else:
        raise NotADirectoryError(path)


if __name__ == "__main__":
    import argparse
    parser = argparse.ArgumentParser(
        description="Watchdog script for watching for files & directories' changes")
    parser.add_argument("path",
                        default=config.WATCH_DIRECTORY,
                        type=is_dir_path,
                        )
    parser.add_argument("-d", "--watch-delay",
                        help=f"Watch delay, default is {config.WATCH_DELAY}",
                        default=config.WATCH_DELAY,
                        type=int,
                        )
    parser.add_argument("-r", "--recursive",
                        action="store_true",
                        help=f"Whether to recursively watch for the path's children, default is {config.WATCH_RECURSIVELY}",
                        default=config.WATCH_RECURSIVELY,
                        )
    parser.add_argument("-p", "--pattern",
                        help=f"Pattern of files to watch, default is {config.WATCH_PATTERN}",
                        default=config.WATCH_PATTERN,
                        )
    parser.add_argument("--watch-directories",
                        action="store_true",
                        help=f"Whether to watch directories, default is {config.DO_WATCH_DIRECTORIES}",
                        default=config.DO_WATCH_DIRECTORIES,
                        )
    # parse the arguments
    args = parser.parse_args()
    # define & launch the log watcher
    log_watcher = LogWatcher(
        watchDirectory=args.path,
        watchDelay=args.watch_delay,
        watchRecursively=args.recursive,
        watchPattern=tuple(args.pattern.split(",")),
        doWatchDirectories=args.watch_directories,
        exceptionPattern=config.EXCEPTION_PATTERN,
    )
    log_watcher.run()