Django problem: RuntimeError: __class__ not set defining 'AbstractBaseUser' as - django

Question

Just upgraded Ubuntu from 18.04 to 20.04 and my Django project failed (it worked fine on Ubuntu 18.04) with the following message:
Exception ignored in thread started by: <function check_errors.<locals>.wrapper at 0x7fc139bd14c0>
Traceback (most recent call last):
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/utils/autoreload.py", line 226, in wrapper
fn(*args, **kwargs)
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/core/management/commands/runserver.py", line 113, in inner_run
autoreload.raise_last_exception()
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/utils/autoreload.py", line 249, in raise_last_exception
six.reraise(*_exception)
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/utils/six.py", line 685, in reraise
raise value.with_traceback(tb)
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/utils/autoreload.py", line 226, in wrapper
fn(*args, **kwargs)
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/__init__.py", line 27, in setup
apps.populate(settings.INSTALLED_APPS)
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/apps/registry.py", line 108, in populate
app_config.import_models(all_models)
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/apps/config.py", line 199, in import_models
self.models_module = import_module(models_module_name)
File "/usr/lib/python3.8/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
File "<frozen importlib._bootstrap>", line 991, in _find_and_load
File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
File "<frozen importlib._bootstrap_external>", line 783, in exec_module
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/contrib/auth/models.py", line 4, in <module>
from django.contrib.auth.base_user import AbstractBaseUser, BaseUserManager
File "/home/yltang/webapps/virtualenv/yltantVenv/lib/python3.8/site-packages/django/contrib/auth/base_user.py", line 52, in <module>
class AbstractBaseUser(models.Model):
RuntimeError: __class__ not set defining 'AbstractBaseUser' as <class 'django.contrib.auth.base_user.AbstractBaseUser'>. Was __classcell__ propagated to type.__new__?
My requirements.txt is as follows:
appdirs==1.4.2
beautifulsoup4==4.5.3
certifi==2018.4.16
chardet==3.0.4
dj-database-url==0.4.2
dj-static==0.0.6
Django==1.10.6
django-toolbelt==0.0.1
gunicorn==19.7.0
idna==2.6
packaging==16.8
psycopg2==2.8.6
pycrypto==2.6.1
pyparsing==2.2.0
requests==2.18.4
rollbar==0.14.0
six==1.10.0
static3==0.7.0
urllib3==1.22
How do I know what caused such an incompatibility problem, and how to fix it?

Answer 1

Look's like an issue with Django 1.10.x and Python 3.6:
https://bugs.python.org/issue23722
https://github.com/django/django/pull/7653/commits/5a36dbc634f4ebd7ccae8f0a4bab987b478750cb
Options are to downgrade Python to version 3.5 or to update Django to newer release.