SystemError: Parent module 'setuptools' not loaded, cannot perform relative import with setuptools 50

After upgrading setuptools to 50.0 today, the environment fails to locate the entry points as it could not import distutils

$ python --version
Python 3.5.1
$ python -c "import distutils"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 666, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 577, in module_from_spec
  File "/home/gchan/tmp/setuptools-python-3.5/lib/python3.5/site-packages/_distutils_hack/__init__.py", line 82, in create_module
    return importlib.import_module('._distutils', 'setuptools')
  File "/home/gchan/tmp/setuptools-python-3.5/lib64/python3.5/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 981, in _gcd_import
  File "<frozen importlib._bootstrap>", line 931, in _sanity_check
SystemError: Parent module 'setuptools' not loaded, cannot perform relative import

The issue could not be found in the python 3.8 environment.

[NicolasPA]

Same issue. Worked around with downgrading and blacklisting 50.0:

pip install "setuptools!=50.0" --force-reinstall

and in requirements.txt:

setuptools!=50.0

[jantman]

For what it’s worth:

1. I’m not terribly new to Python, but the impact of “Once again, Setuptools overrides the stdlib distutils on import.” is completely lost on me, especially when it comes to discovering entrypoints.
2. Whatever this “number of environments” is, by far the biggest impact to me is that my organization heavily uses Python (and setuptools entrypoints) inside of Docker images… and all of our images are based on Debian. I’d expect that many people/organizations are in this same situation (given the popularity of Debian as a base for Docker images) but may not have rebuilt images recently enough for the impact to be discovered.