TypeError: 'NoneType' object is not iterable in _top_level_inferred

[harupy]

Reposting #340 (comment) as an issue.

I'm observing importlib_metadata.packages_distributions() throw the following error:

  File "/opt/mlflow/mlflow/utils/requirements_utils.py", line 129, in <module>
    _MODULE_TO_PACKAGES = importlib_metadata.packages_distributions()
  File "/miniconda/lib/python3.9/site-packages/importlib_metadata/__init__.py", line 1016, in packages_distributions
    for pkg in _top_level_declared(dist) or _top_level_inferred(dist):
  File "/miniconda/lib/python3.9/site-packages/importlib_metadata/__init__.py", line 1026, in _top_level_inferred
    return {

https://github.com/mlflow/mlflow/runs/3428616955#step:5:7078

It looks like the line 1028 in _top_level_inferred tries to iterate on dist.files that can be None and then throws the error above:

importlib_metadata/importlib_metadata/__init__.py

Lines 1025 to 1030 in 15df009

	def _top_level_inferred(dist):
	return {
	f.parts[0] if len(f.parts) > 1 else f.with_suffix('').name
	for f in dist.files
	if f.suffix == ".py"
	}

https://docs.python.org/3/library/importlib.metadata.html#distribution-files says:

In the case where the metadata file listing files (RECORD or SOURCES.txt) is missing, files() will return None. The caller may wish to wrap calls to files() in always_iterable or otherwise guard against this condition if the target distribution is not known to have the metadata present.

[andersk]

I happened to fix this in #342 with:

     @property
-    def files(self):
+    def files(self) -> List[PackagePath]:
…
-        return file_lines and list(starmap(make_file, csv.reader(file_lines)))
+        return list(starmap(make_file, csv.reader(file_lines))) if file_lines else []

Although if the None return is documented, maybe a different fix is needed. (Edit: done.)

[jaraco]

I've yanked the 4.7.0 release from PyPI while I address the issue.