pawfix/PyPaper — reverse-engineered prompt

Build me a small Python app called PyPaper that lets me search for wallpapers online, download one, save it to a folder I choose, and set it as my desktop wallpaper automatically.

I want it to work from the command line, but also open a simple window if the desktop interface dependency is installed. The normal flow should be easy, run the app, search or request a wallpaper, download it, then apply it. Let me choose a save folder, and let advanced users force which wallpaper setter to use. It should mainly support Linux wallpaper tools, but also try to handle Windows and macOS using the usual system commands.

Please keep it lightweight, with minimal dependencies, clean Python files, and a simple install from source using a virtual environment and requirements file. Include helpful command line options, environment variables for default save folder and handler, and clear error messages when a wallpaper tool is missing. Look up current docs online if you need to.