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

[gavincyi]

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.

[aaronlee-xyz]

Found the same issue with python 3.6.1 (pyenv)

[akx]

Same here, Ubuntu 16.04. Seems to be another symptom of #2350.

 SystemError: Parent module 'setuptools' not loaded, cannot perform relative import
   File "<frozen importlib._bootstrap>", line 931, in _sanity_check
   File "<frozen importlib._bootstrap>", line 981, in _gcd_import
     return _bootstrap._gcd_import(name[level:], package, level)
   File "/usr/lib/python3.5/importlib/__init__.py", line 126, in import_module
     return importlib.import_module('._distutils', 'setuptools')
   File "/usr/local/lib/python3.5/dist-packages/_distutils_hack/__init__.py", line 82, in create_module
   File "<frozen importlib._bootstrap>", line 577, in module_from_spec
   File "<frozen importlib._bootstrap>", line 666, in _load_unlocked
   File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
   File "<frozen importlib._bootstrap>", line 969, in _find_and_load
     from distutils.version import StrictVersion
   File "/usr/local/lib/python3.5/dist-packages/redis/connection.py", line 2, in <module>
     from redis.connection import (ConnectionPool, UnixDomainSocketConnection,
   File "/usr/local/lib/python3.5/dist-packages/redis/client.py", line 12, in <module>
     from redis.client import Redis, StrictRedis
   File "/usr/local/lib/python3.5/dist-packages/redis/__init__.py", line 1, in <module>
     from redis import Redis
   [...]

[ThomasDevoogdt]

The same can be said for Matplotlib:

main.py:6: in <module>
    import matplotlib
../venv/lib/python3.5/site-packages/matplotlib/__init__.py:120: in <module>
    import distutils.version
<frozen importlib._bootstrap>:969: in _find_and_load
    ???
<frozen importlib._bootstrap>:958: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:666: in _load_unlocked
    ???
<frozen importlib._bootstrap>:577: in module_from_spec
    ???
../venv/lib/python3.5/site-packages/_distutils_hack/__init__.py:82: in create_module
    return importlib.import_module('._distutils', 'setuptools')
../venv/lib/python3.5/importlib/__init__.py:126: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
<frozen importlib._bootstrap>:981: in _gcd_import
    ???
<frozen importlib._bootstrap>:931: in _sanity_check
    ???
E   SystemError: Parent module 'setuptools' not loaded, cannot perform relative import

[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