This place will call expanduser() on all calls to set_root_path, but I doubt that's what we want to do. The original issue is about interactive user input, I think it's better to put this call immediately after that input is collected instead of inside this setter.

I think we do want it in here since we make a call to pathlib.Path.absolute() which will prepend the current working directory to the path in cases where the path starts with ~, resulting in a root path like /home/jericht/~/tmp/123, which is something we don't want in my opinion.

We are applying os.normpath and pathlib.Path.absolute to the path, so we're already not setting the new_root parameter as is to the self.outputs_by_root dict. To me, this means the code is intended to "make sure the path is a valid root path". However, transforming a path like ~/tmp/123 into something like /the/current/working/dir/~/tmp/123, for example, seems like a bug. If the caller really wants to set a root path like /the/current/working/dir/~/tmp/123 by just passing in ~/tmp/123 while the cwd is /the/current/working/dir/, I think it's reasonable to have the caller pass in the absolute path in this case.

I've updated the function docstring to make it clear that this happens along with the other transformations it applies to new_root.

I tested this locally to make sure expanduser handles some edge cases I could think of correctly. If the path is already has the ~ expanded, it won't attempt to expand it again creating an invalid path. Here are a few tests I ran locally.

>>> def test_expanduser(path: str):
...     print(f"os.path.expanduser: {os.path.expanduser(path)}")
...     print(f"pathlib.Path.expanduser: {pathlib.Path(path).expanduser()}")
... 

>>> test_expanduser("~/tmp/123")
os.path.expanduser: /home/jericht/tmp/123
pathlib.Path.expanduser: /home/jericht/tmp/123

>>> test_expanduser("~/~/tmp/123")
os.path.expanduser: /home/jericht/~/tmp/123
pathlib.Path.expanduser: /home/jericht/~/tmp/123

>>> test_expanduser("/tmp/~/123")
os.path.expanduser: /tmp/~/123
pathlib.Path.expanduser: /tmp/~/123

>>> test_expanduser("/home/jericht/~/tmp/123")
os.path.expanduser: /home/jericht/~/tmp/123
pathlib.Path.expanduser: /home/jericht/~/tmp/123

>>> test_expanduser("~/home/jericht/~/tmp/123")
os.path.expanduser: /home/jericht/home/jericht/~/tmp/123
pathlib.Path.expanduser: /home/jericht/home/jericht/~/tmp/123

side comment: Does this change also work for deadline attachment download ?

If we do want this expansion to happen always in the setter, I think we should look more closely at where the value comes from currently, and where it could come from. Will this be surprising in any case?