Possible bug introduced with PR250, joinpath with "." causes StopIteration

[VolkerH]

Consider the following code snippet:

stopiteration_bug.py:

import spacem_maldi.Ontologies
from importlib_resources import files

print(files(spacem_maldi.Ontologies) / ".")

With importlib-resources<=5.7.1 this produces the following output:

/home/hilsenst/GitlabEMBL/spacem-ht/src/spacem-maldi/spacem_maldi/Ontologies

Starting from version 5.8.0, i.e. after PR #250 this throws a StopIteration exception:

~/Untracked$ python stopiteration_bug.py 
Traceback (most recent call last):
  File "stopiteration_bug.py", line 5, in <module>
    print(files(spacem_maldi.Ontologies) / ".")
  File "/home/hilsenst/miniconda3/envs/spacem-maldi-control/lib/python3.8/site-packages/importlib_resources/abc.py", line 130, in __truediv__
    return self.joinpath(child)
  File "/home/hilsenst/miniconda3/envs/spacem-maldi-control/lib/python3.8/site-packages/importlib_resources/readers.py", line 87, in joinpath
    return super().joinpath(*descendants)
  File "/home/hilsenst/miniconda3/envs/spacem-maldi-control/lib/python3.8/site-packages/importlib_resources/abc.py", line 114, in joinpath
    target = next(names)
StopIteration

The spacem_maldi package is a private package, but I don't think that is relevant here. If needed I can try and create a minimal public package.

[blackadar]

+1, there should be a way to get the Pathlib Path without joinpath anyways.

Also, a workaround for now:

print((files(spacem_maldi.Ontologies) / "fakefilename.txt").parent)

[VolkerH]

there should be a way to get the Pathlib Path without joinpath anyways

Yes, I felt that / "." was a crutch to start with but couln't find a better (proper) way.

[jaraco]

Oh, you shouldn't rely on joinpath to get a materialized path. If what you need is a materialized path on the file system, use as_file(traversable). files() returns a Traversable and Traversable.joinpath also returns a Traversable, which may or may not be on the filesystem. Although depending on your usage, you may not need to materialize the traversable at all and you may be able to get the value directly from the Traversable (such as with .open or .read_text()).

Still, you shouldn't get a StopIteration by attempting to join a path.

[jaraco]

I'm unable to replicate the issue:

>>> import importlib_resources as resources
>>> print(resources.files('importlib_resources') / ".")
/Users/jaraco/code/python/importlib_resources/importlib_resources

What's special about spacem_maldi.Ontologies that triggers the issue?

[jaraco]

I thought maybe the issue was that Ontologies was a directory without an __init__, but I'm still unable to trigger the failure:

>>> import pathlib
>>> pathlib.Path('importlib_resources/foo').mkdir()
>>> print(resources.files('importlib_resources.foo') / ".")
/Users/jaraco/code/python/importlib_resources/importlib_resources/foo

[jaraco]

Since the issue isn't reproducible, I'm closing it, but feel free to follow-up with the requested info and we can investigate further.