Eh, I write a lot of Python and while it's unnecessary, it can make code easier to read if not overused.

  if (config_fn := base_dir / "config").exists():
      ...

is just a tiny bit shorter than this:

  config_fn = base_dir / "config"
  if config_fn.exists():
      ...

but if you do this enough times (if you are handling a lot of possible errors / missing data, etc.) it can definitely shorten the code.