How to Watch a Directory for New Files in Python

import time
import os
from pathlib import Path

WATCH_DIR = Path("watched_files")

def watch_for_new_files(directory: Path, sleep_time: float = 1.0, max_iterations: int = 10):
    """Poll a directory for new files and print when one appears."""
    directory.mkdir(exist_ok=True)
    existing = set(os.listdir(directory))
    
    print(f"Watching {directory} for new files...")
    for iteration in range(max_iterations):
        time.sleep(sleep_time)
        current = set(os.listdir(directory))
        new_files = current - existing
        if new_files:
            for file in sorted(new_files):
                print(f"New file detected: {file}")
            existing = current
        else:
            print(f"Check {iteration + 1}: no new files yet")
    
    print("Finished watching.")

if __name__ == "__main__":
    # Create a demo file after 2 seconds to show detection
    import threading
    
    def add_demo_file():
        time.sleep(2)
        (WATCH_DIR / "demo.txt").write_text("Hello from demo!")
    
    thread = threading.Thread(target=add_demo_file, daemon=True)
    thread.start()
    
    watch_for_new_files(WATCH_DIR, sleep_time=0.5, max_iterations=10)