New submission from David Robertson <david.m.roberts...@gmail.com>:
Originally written up at the typeshed repo: https://github.com/python/typeshed/issues/7513. The conclusion was that this is a bug in the implementation rather than an incorrect annotation. To my surprise, I discovered in https://github.com/matrix-org/synapse/issues/12223 that it is possible for `importlib.metadata.version(...)` to return `None`. To reproduce this: 1. Create a new virtual environment. I'm using CPython 3.10.2 as my interpreter. 2. Within the venv, `pip install bottle`. (Any package will do; I choose `bottle` because it's small and doesn't have any dependencies). 3. Check importlib reports the `version` of `bottle`: ```python >>> import importlib.metadata as m >>> m.version('bottle') '0.12.19' ``` 4. Here's the dirty bit: remove the metadata files for that package but keep the metadata directory. - Use `pip show bottle` to find the `site-packages` location - From there, remove all files in the `bottle-VERSION-.dist-info` directory: `rm /path/to/site-packages/bottle-VERSION.dist-info/*'. 5. The `version` of `bottle` is now judged to be `None`: ```python >>> import importlib.metadata as m >>> m.version("bottle") is None True ``` `pip show bottle` now determines that `bottle` isn't installed: ```shell $ pip show bottle WARNING: Package(s) not found: bottle ``` As well as importlib.metadata.version, importlib.metadata.Distribution.version and importlib.metadata.Distribution.name return None in this situation. I couldn't see any suggestion in the stdlib docs (https://docs.python.org/3.10/library/importlib.metadata.html#distribution-versions) that this was possible. (Aside: it'd be great if the docs mention that PackageNotFoundError is raised if a package is not installed.) No-one in their right mind should do step 4 willingly, but I have seen it happen in the wild (https://github.com/matrix-org/synapse/issues/12223). We suspected a botched backup or similar was to blame. I'm not familiar with all the machinery of Python package management, but I think I'd expect there to be a PackageNotFoundError raised in this situation? (I can imagine a package that doesn't declare its version, where `version()` returning `None` might make sense; but that feels odd.) Is the behaviour as intended? It looks like this might be related to https://github.com/python/importlib_metadata/issues/371? ---------- components: Library (Lib) messages: 415516 nosy: David Robertson priority: normal severity: normal status: open title: importlib.metadata.version can return None type: behavior versions: Python 3.10 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue47060> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
