When a FileNotFoundError is raised inside while the importlib.resources.path context manager is active a RuntimeError is raised.
Looking at the (3.8) code it seems that FileNotFound exceptions are handled specially from all other exceptions which may lead to this behaviour. While the code in 3.9 changed significantly the same behaviour can be observed.

Files:
.
└── my_package
    ├── data.txt (empty)
    ├── __init__.py (empty)
    └── test.py

Content of test.py:
import importlib.resources
def main():
    with importlib.resources.path('my_package', 'data.txt') as p:
        raise FileNotFoundError()
if __name__ == '__main__':
    main()

Exact error message:
RuntimeError: generator didn't stop after throw()

I can reproduce this. From what I can see the issue is that `importlib.resources.path` intentionally suppresses `FileNotFoundError` errors.

https://github.com/python/cpython/blob/main/Lib/importlib/resources.py#L138

Based on `importlib.resources.path` docstring I think this is to avoid raising an exception if the file is deleted before the context manager exits.

On contextlib.py, since type is not None, it will try to throw the exception but since it's supressed nothing will happen and the code will reach the end by raising the RuntimeError.

https://github.com/python/cpython/blob/main/Lib/contextlib.py#L151

If I'm not mistaken, this is the test that verifies that behaviour: https://github.com/python/cpython/blob/main/Lib/test/test_importlib/test_path.py#L51


I'm not a core dev but it looks like it's an intentional behaviour.

Maybe the docs should be more clear about this. It's not obvious to me when I read the docs.

This was fixed in https://github.com/python/cpython/pull/22915. It can be closed now.

Yes I understand that the function handles this specially to not raise an exception if the file is not found in the package (even though the intention behind this is not clear to me). However if a user causes a FileNotFoundException itself inside of the context manager everything breaks (e.g. does something erroneous with the path, calls subprocess.run with a non existing binary etc).

The supress(FileNotFoundError) context manager now is only active when fetching the file, not during importlib.resources.path. _path_from_resource_path is not longer a generator, so supress(FileNotFoundError) is promptly closed after the return, preventing its side effects from leaking outside the function.

Your reproducible now works as intended:

Traceback (most recent call last):
  File "/home/anubis/git/cpython/test.py", line 9, in <module>
    main()
  File "/home/anubis/git/cpython/test.py", line 6, in main
    raise FileNotFoundError()
FileNotFoundError

Thanks for tracking this down, Filipe. Agreed it sounds like it's fixed in Python 3.10. It's unlikely the fix will be backported to Python 3.9. Instead, if this behavior affects your usage, consider using the `importlib_resources` backport, which also includes the fix. And please follow-up if there are issues not addressed by this approach.

Thanks for looking into it. Yes I can confirm that `importlib_resources` has the expected behaviour - I did not download Python 3.10 as the code seems to be the same.