Detect file creation with watchdog

Finally, after taking a look at the watchdog implementation, it is not necessary to call unschedule_all before stop, this is done automatically. Removing the line containing this method call fixes the issue and the application is running perfectly.

Also, the below script is used to observe filename at a specific path using the PatternMatchingEventHandler.

import time
from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
from watchdog.events import PatternMatchingEventHandler
import sys


class Watcher:
    def __init__(self, path, filename):
        self.observer = Observer()
        self.path = path
        self.filename = filename

    def run(self):
        event_handler = Handler(self.filename)
        self.observer.schedule(event_handler, self.path, recursive=True)
        self.observer.start()
        try:
            while True:
                time.sleep(1)
        except:
            self.observer.stop()
            print("Error")

        self.observer.join()


class Handler(PatternMatchingEventHandler):
    def __init__(self, filename):
        super(Handler, self).__init__(
            patterns=[filename],
            ignore_patterns=["*.tmp"],
            ignore_directories=True,
            case_sensitive=False,
        )

    def on_any_event(self, event):
        print(
            "[{}] noticed: [{}] on: [{}] ".format(
                time.asctime(), event.event_type, event.src_path
            )
        )


if __name__ == "__main__":
    path = "."
    filename = "test.csv"

    w = Watcher(path, filename)
    w.run()

output:

[Tue Feb  9 01:55:38 2021] noticed: [created] on: [/Users/mt/Documents/stackoverflow/test.csv] 
[Tue Feb  9 01:55:44 2021] noticed: [modified] on: [/Users/mt/Documents/stackoverflow/test.csv] 
[Tue Feb  9 01:56:01 2021] noticed: [deleted] on: [/Users/mt/Documents/stackoverflow/test.csv] 

It is also possible to determine the creation of a new file without installing additional libraries.

import os
import time


def watch_file(filename, time_limit=3600, check_interval=60):
    """Return true if filename exists, if not keep checking once every check_interval seconds for time_limit seconds.
    time_limit defaults to 1 hour
    check_interval defaults to 1 minute
    """
    now = time.time()
    last_time = now + time_limit
    
    while time.time() <= last_time:
        if os.path.exists(filename):
            return True
        else:
            # Wait for check interval seconds, then check again.
            time.sleep(check_interval)
    return False


if __name__ == "__main__":
    filename = "test.csv"
    time_limit = 60
    check_interval = 1

    if watch_file(filename, time_limit, check_interval):
        print(f"File created: {os.path.abspath(filename)}")
    else:
        print(
            f"File {filename} not found after waiting: {time_limit} seconds!"
        )

output:

File created: /Users/mt/Documents/stackoverflow/test.csv