Calling `importlib_resources.files` with an editable install fails

[GarrStau]

When calling importlib_resources.files("sample-namespace") to retrieve a text file, an exception is thrown if an editable install has been done for the package.

I am able to trigger this with a relatively simple setup - I have a namespace package with two files, sample.txt and a __main__.py that has two lines:
from importlib_resources import files
files("sample-namespace")

In a venv with only importlib_resources 6.4.0 installed, calling "py -m sample-namespace" works without issue if sample-namespace is not installed or normally installed, but will fail if it is installed in editable mode.

The error is thrown in the MultiplexedPath constructor, because '__editable__.sample_namespace-1.0.finder.__path_hook__' is one of the paths provided, and path.is_dir() is False leading to raising NotADirectoryError.

I'm not convinced that I'm doing everything right, but I don't know of any limitations with editable installs. I'm not very familiar with this library, but if there's anything I can do to help, let me know.

Thank you!

(.venv) PS C:\git\TEST\test-importlib-resources-files-editable> py -m sample-namespace
Traceback (most recent call last):
 File "<frozen runpy>", line 198, in _run_module_as_main
 File "<frozen runpy>", line 88, in _run_code
 File "C:\git\TEST\test-importlib-resources-files-editable\sample-namespace\__main__.py", line 3, in <module>
 files("sample-namespace")
 File "C:\git\TEST\test-importlib-resources-files-editable\.venv\Lib\site-packages\importlib_resources\_common.py", line 46, in wrapper
 return func(anchor)
 ^^^^^^^^^^^^
 File "C:\git\TEST\test-importlib-resources-files-editable\.venv\Lib\site-packages\importlib_resources\_common.py", line 56, in files
 return from_package(resolve(anchor))
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\git\TEST\test-importlib-resources-files-editable\.venv\Lib\site-packages\importlib_resources\_common.py", line 116, in from_package
 reader = spec.loader.get_resource_reader(spec.name)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\git\TEST\test-importlib-resources-files-editable\.venv\Lib\site-packages\importlib_resources\future\adapters.py", line 66, in get_resource_reader
 or super().get_resource_reader(name)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\git\TEST\test-importlib-resources-files-editable\.venv\Lib\site-packages\importlib_resources\_adapters.py", line 29, in get_resource_reader
 return CompatibilityFiles(self.spec)._native()
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\git\TEST\test-importlib-resources-files-editable\.venv\Lib\site-packages\importlib_resources\_adapters.py", line 153, in _native
 reader = self._reader
 ^^^^^^^^^^^^
 File "C:\git\TEST\test-importlib-resources-files-editable\.venv\Lib\site-packages\importlib_resources\_adapters.py", line 147, in _reader
 return self.spec.loader.get_resource_reader(self.spec.name)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "<frozen importlib._bootstrap_external>", line 1425, in get_resource_reader
 File "C:\Users\garrstau\AppData\Local\Programs\Python\Python312\Lib\importlib\resources\readers.py", line 133, in __init__
 self.path = MultiplexedPath(*list(namespace_path))
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Users\garrstau\AppData\Local\Programs\Python\Python312\Lib\importlib\resources\readers.py", line 70, in __init__
 raise NotADirectoryError('MultiplexedPath only supports directories')
NotADirectoryError: MultiplexedPath only supports directories

[jaraco]

I recently encountered this error too in jaraco.imaging. The same code previously passed on Apr 24, so my guess is there was some regression since then.

[jaraco]

For what it's worth, editable installs used to work, but not since the path hook was added to the namespace path (probably a newer form of editable install).

Here's what I'm seeing for namespace path:

> /opt/homebrew/Cellar/python@3.12/3.12.5/Frameworks/Python.framework/Versions/3.12/lib/python3.12/importlib/resources/readers.py(133)__init__()
-> self.path = MultiplexedPath(*list(namespace_path))
(Pdb) namespace_path
_NamespacePath(['/Users/jaraco/code/jaraco/jaraco.imaging/.tox/py/lib/python3.12/site-packages/jaraco', '/Users/jaraco/code/jaraco/jaraco.imaging/jaraco', '__editable__.jaraco.imaging-2.1.1.dev173+gbde5bcf.finder.__path_hook__'])
(Pdb) import jaraco
(Pdb) jaraco.__path__
_NamespacePath(['/Users/jaraco/code/jaraco/jaraco.imaging/.tox/py/lib/python3.12/site-packages/jaraco', '/Users/jaraco/code/jaraco/jaraco.imaging/jaraco', '__editable__.jaraco.imaging-2.1.1.dev173+gbde5bcf.finder.__path_hook__'])

@abravalheri Do you know what it is that's adding that __editable__ entry to the _NamespacePath? Is there a spec that allows that path to be something other than an importable path? What should importlib_resources be doing (if anything) to honor that path entry?

[jaraco]

Oh, I see pypa/setuptools#3548 is already tracking the issue.

[abravalheri]

Do you know what it is that's adding that editable entry to the _NamespacePath? Is there a spec that allows that path to be something other than an importable path?

This is added by a .pth file added on purpose by the editable_wheel command in setuptools to the editable wheel. The objective is to trigger a PathEntryFinder, which is so far the only known way in the community to implement namespace packages via import finders. The entry added to sys.path is a path item... but not a conventional one: it is a path that does not exist but is there only to force the PathEntryFinder to be called.

I believe that the standard that supports this is PEP 302. In the text of the PEP it is suggested that adding a "non existing" path is an acceptable approach for a different class of problems (but nonetheless the approach described still adds a non existing file to sys.path):

For now, if a hook is required after sys.path has been processed, it can be simulated by adding an arbitrary “cookie” string at the end of sys.path, and having the required hook associated with this cookie, via the normal sys.path_hooks processing. In the longer term, the path handling code will become a “real” hook on sys.meta_path, and at that stage it will be possible to insert user-defined hooks either before or after it.

The Python docs also explicitly say:

...
Most path entries name locations in the file system, but they need not be limited to this.
...
sys.path contains a list of strings providing search locations for modules and packages. It is initialized from the PYTHONPATH environment variable and various other installation- and implementation-specific defaults. Entries in sys.path can name directories on the file system, zip files, and potentially other “locations” (see the site module) that should be searched for modules, such as URLs, or database queries. Only strings should be present on sys.path; all other data types are ignored.

Also here in https://docs.python.org/3/reference/import.html#finders-and-loaders:

The import path is a list of locations that may name file system paths or zip files. It can also be extended to search for any locatable resource, such as those identified by URLs.

So my interpretation is that sys.path can contain all sorts of stuff that are searched by finders/loaders. The text even mentions database queries, which is a pretty good example of not a regular file path. Nevertheless, since there is an associated PathEntryFinder, these entries work effectively as an "importable path" but not in the conventional sense.

What should importlib_resources be doing (if anything) to honor that path entry?

I am not sure here. PEP 320 mentions loader.get_data(path). I did not implement any custom loader in setuptools, just the finders that rely on standard functions of importlib, so all the loaders produced should also be fairly standard. Maybe the standard loaders of importlib implement the get_data protocol?

Another thought is that sometimes editable namespace packages do not correspond to an actual directory in disk, and it is only simulated by the importlib machinery. For example, consider that a developer uses package_dir in setuptools to remap the file paths and point package a.b.c to a project folder called x. We can map a.b.c to the existing x folder, but there is no correspondence for a or a.b.

In that case, users are better off if they avoid calling importlib_resources.files("a"). Instead, they will have to be more specific and call importlib_resources.files("a.b.c").

---

I believe that pypa/setuptools#3548 regards a different original problem.

To be honest, since we never got a reproducer, I believe that the original problem might be caused by another piece of software that expects all entries of sys.path to be existing regular paths to files or directories (and as explained above that is not how it is described by the Python docs). And if that is the case there is not much to be done by setuptools itself.

[abravalheri]

but I don't know of any limitations with editable installs.

@GarrStau , there is a non-exhaustive list in https://setuptools.pypa.io/en/latest/userguide/development_mode.html#limitations.

[jaraco]

That helps a lot. Thanks for the context. I do believe it makes sense for importlib resources to support this mode, and it should continue to be possible to resolve resources from a namespace package (as long as some provider provides resources from that package).

[jaraco]

It wasn't too hard to create a test that captures the failure (b06b5fb), but unfortunately, its traceback reveals another problem:

________________________________________________ OpenNamespaceTests.test_non_paths_in_dunder_path _________________________________________________

self = <importlib_resources.tests.test_files.OpenNamespaceTests testMethod=test_non_paths_in_dunder_path>

 @pytest.mark.xfail(reason="#311")
 def test_non_paths_in_dunder_path(self):
 """
 Non-path items in a namespace package's ``__path__`` are ignored.
 
 As reported in python/importlib_resources#311, some tools
 like Setuptools, when creating editable packages, will inject
 non-paths into a namespace package's ``__path__``, a
 sentinel like
 ``__editable__.sample_namespace-1.0.finder.__path_hook__``
 to cause the ``PathEntryFinder`` to be called when searching
 for packages. In that case, resources should still be loadable.
 """
 import namespacedata01
 
 namespacedata01.__path__.append(
 '__editable__.sample_namespace-1.0.finder.__path_hook__'
 )
 
> resources.files(namespacedata01)

importlib_resources/tests/test_files.py:84: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
importlib_resources/_common.py:46: in wrapper
 return func(anchor)
importlib_resources/_common.py:56: in files
 return from_package(resolve(anchor))
importlib_resources/_common.py:117: in from_package
 reader = spec.loader.get_resource_reader(spec.name)
importlib_resources/future/adapters.py:66: in get_resource_reader
 or super().get_resource_reader(name)
importlib_resources/_adapters.py:29: in get_resource_reader
 return CompatibilityFiles(self.spec)._native()
importlib_resources/_adapters.py:153: in _native
 reader = self._reader
importlib_resources/_adapters.py:147: in _reader
 return self.spec.loader.get_resource_reader(self.spec.name)
<frozen importlib._bootstrap_external>:1425: in get_resource_reader
 ???
/opt/homebrew/Cellar/python@3.12/3.12.5/Frameworks/Python.framework/Versions/3.12/lib/python3.12/importlib/resources/readers.py:133: in __init__
 self.path = MultiplexedPath(*list(namespace_path))
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = MultiplexedPath('/private/var/folders/f2/2plv6q2n7l932m2x004jlw340000gn/T/tmp2ubfwwvu/namespacedata01', '__editable__.sample_namespace-1.0.finder.__path_hook__')
paths = ('/private/var/folders/f2/2plv6q2n7l932m2x004jlw340000gn/T/tmp2ubfwwvu/namespacedata01', '__editable__.sample_namespace-1.0.finder.__path_hook__')

 def __init__(self, *paths):
 self._paths = list(map(pathlib.Path, remove_duplicates(paths)))
 if not self._paths:
 message = 'MultiplexedPath must contain at least one path'
 raise FileNotFoundError(message)
 if not all(path.is_dir() for path in self._paths):
> raise NotADirectoryError('MultiplexedPath only supports directories')
E NotADirectoryError: MultiplexedPath only supports directories

/opt/homebrew/Cellar/python@3.12/3.12.5/Frameworks/Python.framework/Versions/3.12/lib/python3.12/importlib/resources/readers.py:70: NotADirectoryError

The error is coming from importlib.resources, meaning that importlib_resources' readers aren't taking precedence, so it won't be possible to fix the issue strictly in importlib_resources without first making sure that the local readers take precedence.

[jaraco]

I do see that importlib_resources.future.adapters.TraversableResourcesLoader.get_resource_reader is getting to super().get_resource_reader(name), so ._standard_reader() would have to have been called before that, so it's probably just the case that _namespace_reader is not resolving because of this reported issue. That is, there's probably a ValueError on line 149:

importlib_resources/importlib_resources/readers.py

Lines 140 to 150 in d021417

	@classmethod
	def _resolve(cls, path_str) -> abc.Traversable:
	r"""
	Given an item from a namespace path, resolve it to a Traversable.
	path_str might be a directory on the filesystem or a path to a
	zipfile plus the path within the zipfile, e.g. ``/foo/bar`` or
	``/foo/baz.zip/inner_dir`` or ``foo\baz.zip\inner_dir\sub``.
	"""
	(dir,) = (cand for cand in cls._candidate_paths(path_str) if cand.is_dir())
	return dir

And that's causing the namespace reader to be skipped.

So, fixing the root issue might also address the secondary issue.

[jaraco]

So, fixing the root issue might also address the secondary issue.

And indeed it does.