Reload only working when app is supplied as string

[soslan]

Hi! I am tinkering with programmatic start of uvicorn server, and encountered this unexpected behavior. When I supply an ASGIApplication to Config(), reload functionality is not working because should_reload checks whether self.app is a string and returns False:

https://github.com/encode/uvicorn/blob/90f43699c79bcd2b0676186fc6d3b9baf679d3c8/uvicorn/config.py#L528-L530

Instead of working reload functionality, I see this:

https://github.com/encode/uvicorn/blob/90f43699c79bcd2b0676186fc6d3b9baf679d3c8/uvicorn/config.py#L281-L284

But there is nothing in the docs that mentions what conditions are required for the reload to work.

Is this a bug or reload only works with str-defined app for a reason? If it is a bug, I am willing to contribute by fixing it.

[Kludex]

If the string is provided, uvicorn will try to import it. If it's the app itself, it will try to use it, but reload runs on another process.

I think... If you can make a way to pass the app location as string to the reloader, then it would work.

But it's expected as of today.

[Blotz]

It seems the ASGIApplication object doesn't expose the source code path __file__, __path__, preventing Uvicorn from automatically detecting changes for reloading. A workaround would be to allow users to explicitly specify directories to watch via a reload_dirs parameter. For example:

app = FastAPI()

...

paths = [str(pathlib.Path().resolve())]  # for example, find path to current folder
uvicorn.run(app, reload=True, reload_dirs=paths)

This would be especially useful for Python packages. It would allow starting a Uvicorn server using python -m <package_name> without requiring the package to import itself or use some cli tool to call it.