Postinstall for python@3.7 fails (tested on multiple machines)

[sseneca]

brew config output

HOMEBREW_VERSION: 3.5.7
ORIGIN: https://github.com/Homebrew/brew
HEAD: ce8ef89ec0cfe875c48c3a83a843af9074c05930
Last commit: 3 days ago
Core tap ORIGIN: https://github.com/Homebrew/homebrew-core
Core tap HEAD: b9dc7e988ae2f94de6c200dddf37bd99e8994a40
Core tap last commit: 18 minutes ago
Core tap branch: master
HOMEBREW_PREFIX: /usr/local
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: /private/tmp/com.apple.launchd.Yc6ELhTu1O/org.xquartz:0
HOMEBREW_EDITOR: nvim
HOMEBREW_MAKE_JOBS: 8
HOMEBREW_NO_ENV_HINTS: set
Homebrew Ruby: 2.6.8 => /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby
CPU: octa-core 64-bit icelake
Clang: 13.1.6 build 1316
Git: 2.37.1 => /usr/local/bin/git
Curl: 7.79.1 => /usr/bin/curl
macOS: 12.5-x86_64
CLT: 13.4.0.0.1.1651278267
Xcode: 13.4.1

brew doctor output

Please note that these warnings are just used to help the Homebrew maintainers
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Warning: Putting non-prefixed coreutils in your path can cause GMP builds to fail.

Verification

• I ran brew update and am still able to reproduce my issue.
• I have resolved all warnings from brew doctor and that did not fix my problem.

What were you trying to do (and why)?

Install Python 3.7. Because I want to use Python 3.7

What happened (include all command output)?

==> Postinstalling python@3.7
==> /usr/local/Cellar/python@3.7/3.7.13_1/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python@3.7/3.7.13_1/bin --install-lib=/usr/local/lib/python3.7/site-packages --single-version-externally-managed -
==> /usr/local/Cellar/python@3.7/3.7.13_1/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python@3.7/3.7.13_1/bin --install-lib=/usr/local/lib/python3.7/site-packages --single-version-externally-managed -
==> /usr/local/Cellar/python@3.7/3.7.13_1/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python@3.7/3.7.13_1/bin --install-lib=/usr/local/lib/python3.7/site-packages --single-version-externally-managed -
==> /usr/local/Cellar/python@3.7/3.7.13_1/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python@3.7/3.7.13_1/bin --install-lib=/usr/local/lib/python3.7/site-packages --single-version-externally-managed -
Last 15 lines from /Users/sseneca/Library/Logs/Homebrew/python@3.7/post_install.04.python3:
  File "/usr/local/lib/python3.7/site-packages/setuptools/_distutils/dist.py", line 293, in __init__
    self.finalize_options()
  File "/usr/local/lib/python3.7/site-packages/setuptools/dist.py", line 852, in finalize_options
    ep(self)
  File "/usr/local/lib/python3.7/site-packages/setuptools/dist.py", line 869, in _finalize_setup_keywords
    for ep in metadata.entry_points(group='distutils.setup_keywords'):
  File "/usr/local/lib/python3.7/site-packages/setuptools/_vendor/importlib_metadata/__init__.py", line 999, in entry_points
    return SelectableGroups.load(eps).select(**params)
  File "/usr/local/lib/python3.7/site-packages/setuptools/_vendor/importlib_metadata/__init__.py", line 449, in load
    ordered = sorted(eps, key=by_group)
  File "/usr/local/lib/python3.7/site-packages/setuptools/_vendor/importlib_metadata/__init__.py", line 997, in <genexpr>
    dist.entry_points for dist in unique(distributions())
  File "/usr/local/lib/python3.7/site-packages/setuptools/_vendor/importlib_metadata/_itertools.py", line 16, in unique_everseen
    k = key(element)
AttributeError: 'PathDistribution' object has no attribute '_normalized_name'
Warning: The post-install step did not complete successfully
You can try again using:
  brew postinstall python@3.7

What did you expect to happen?

For it to install Python 3.7

Step-by-step reproduction instructions (by running brew commands)

brew install python@3.7
# fails with above error, as does running brew postinstall python@3.7

[triallax]

This sounds like python/importlib_metadata#396, which already has a PR open: python/importlib_metadata#397

[cho-m]

This should be a side effect of current setuptools_scm that has a bootstrap loop. My previous analysis in #104489 (comment)

One workaround is to restrict setuptools_scm[toml] to <7.

Note that we currently aren't able to update to latest importlib_metadata in python@3.7 since the build system switched from having setup.py to only having setup.cfg/pyproject.toml, so it cannot be installed via old python3 setup.py ....

[cho-m]

Alternatively, we might be able to just drop the resources for importlib_metadata and zipp.

They were originally added to support virtualenv package for Homebrew's DSL (#64831) but we switched DSL to use built-in -m venv just afterward in Homebrew/brew#10039.

Seems like easier option. Users can then use pip to install wheels in an upstream-supported manner.

---

Note that there is still a build loop when using Homebrew DSL for formulae like ansible@2.8, but that is unavoidable due to setuptools_scm upstream no longer allowing our bootstrap-style installation in Python <= 3.7

In core tap, we no longer use python@3.7 so isn't really an issue. Users that directly run pip won't see any issue since it will install wheels.