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packages_distributions relies on setuptools implementation detail #526
Description
This is a follow-up to #402.
packages_distributions reads top_level.txt to determine the names. This file isn't part of any PEP and to my knowledge only implemented by setuptools, as a historical artifact from eggs. This leads users to believe that build backends not supporting this function have a bug (astral-sh/uv#16423).
Would it be possible to update the documentation to accurately reflect that this is not a problem with some PEP 660 build backends not supplying top-level names, but that this function is generally not expected to work with editable installs at all, with the historical exception of setuptools?
(This may change with PEP 794)
importlib_metadata/importlib_metadata/__init__.py
Lines 1133 to 1134 in 95ecf2a
Activity
jaraco commentedon Dec 29, 2025
I'd accept a pull request to document this limitation. I would like to see some proper, formal support for a package to represent deterministically the top-level names that it exposes.
stefanor commentedon Jan 5, 2026
That is at least used in a context where the file not existing is probably not a problem:
importlib_metadata/importlib_metadata/__init__.py
Line 1144 in d8a7576
I wouldn't say it's relying on this file.
konstin commentedon Jan 5, 2026
I consider it a bug in the sense it makes an importlib function rely on non-spec behavior of setuptools. See the uv bug for an MRE, where a user ran into a specific case where it doesn't work when not using setuptools: astral-sh/uv#16423
bunny-therapist commentedon Jul 3, 2026
Shouldn't this function be updated now that PEP 794 has been accepted?
It seems like both in
importlib_metadataand in cpython itself, nothing has changed inpackages_distributions?molloyzak13 commentedon Jul 3, 2026
reply_target: #526
PEP 794 replaces what
top_level.txtdoes, but build backends need to ship the new dist-info metadata first. until they do,packages_distributions()is stuck reading the old file. not really a bug in importlib_metadata, just waiting on the ecosystem side.bunny-therapist commentedon Jul 6, 2026
PEP 794 is supported by
It looks like setuptools does not have it yet, but they have an issue and a PR
Is it setuptools that importlib_metadata is waiting for? Is this planned? I would expect importlib_metadata to eventually read metadata according to PEP 794 with the old functionality (top_level.txt) as a fallback.