Sometimes you want to run code automatically when files change, like rebuild assets, trigger a script, or just keep an eye on what’s happening in a directory. Instead of constantly polling or writing your own file watcher, Python’s watchdog library makes this painless. How it works under the hood Operating systems already provide mechanisms to signal when files change: Linux: inotify macOS: FSEvents Windows: ReadDirectoryChangesW Watchdog doesn’t reinvent the wheel. It wraps these low-level APIs in a Python layer, normalizes the events, and hands them to you via a callback system.