In some import sequence ./manage.py raises "populate() isn't reentrant" hiding the original error

[living-dev]

Hi,

I often add other command line entry points to my project, as a consequence, I ensure that whenever some code use my project code, all the django part is initialized if not already done. This can lead to a import sequence by manage.py that hides the real error.

Here is a reproduction scenario:

$ python -m venv bug
$ cd bug/
$ . ./bin/activate
$ pip install django==5.2.5
$ django-admin startproject bug
$ cd bug
$ ./manage.py startapp an_app
$ ./manage.py startapp bad_import

Add "an_app" and "bad_import" to INSTALLED_APPS:

INSTALLED_APPS = [
...
    'an_app',
    'bad_import',
]

Here the automatic django initialization code:

$ cat > bug/__init__.py << EOF
import os

import django

from django.conf import settings
from django.apps import apps
if not settings.configured and not apps.loading:
    os.environ['DJANGO_SETTINGS_MODULE'] = 'bug.settings'
    django.setup()
EOF

And a custom entry point under bug project:

$ cat > bug/cli.py << EOF
from django.conf import settings
if __name__ == '__main__':
    print('My CLI entry point:', settings.configured)
EOF

At this point both cli and manage.py are working:

$ python -m bug.cli
My CLI entry point: True
$ ./manage.py 
Type 'manage.py help <subcommand>' for help on a specific subcommand.
...

Now we introduce a bad import line because of typo error in the models:

$ echo 'import an_app.model' >> bad_import/models.py

When using our cli entry point, the error is clear:

$ python -m bug.cli
Traceback (most recent call last):
...
  File "/home/debian/Support/django/bug-20250807/bug/bug/bug/__init__.py", line 9, in <module>
    django.setup()
...
  File "/home/debian/Support/django/bug-20250807/bug/bug/bad_import/models.py", line 3, in <module>
    import an_app.model
ModuleNotFoundError: No module named 'an_app.model'

But when we use manage.py, the error is hidden:

$ ./manage.py 
Traceback (most recent call last):
...
  File "/home/debian/Support/django/bug-20250807/bug/lib/python3.11/site-packages/django/core/management/__init__.py", line 416, in execute
    django.setup()
  File "/home/debian/Support/django/bug-20250807/bug/lib/python3.11/site-packages/django/__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/home/debian/Support/django/bug-20250807/bug/lib/python3.11/site-packages/django/apps/registry.py", line 83, in populate
    raise RuntimeError("populate() isn't reentrant")
RuntimeError: populate() isn't reentrant

In fact the error is memorized in django/core/management/__init__.py:381:

        try:
            settings.INSTALLED_APPS
        except ImproperlyConfigured as exc:
            self.settings_exception = exc
        except ImportError as exc:
            self.settings_exception = exc

But we finish on this part, that triggers the reentrant populate django/core/management/__init__.py:414:

            # In all other cases, django.setup() is required to succeed.
            else:
                django.setup()

I think it could be simply resolved by propagating the memorized exception if django.setup() fails, so the trace is more explicit:

            # In all other cases, django.setup() is required to succeed.
            else:
                try:
                    django.setup()
                except Exception as exc:
                    raise exc from self.settings_exception

In this case the stack trace can help as it shows both the original error and that we also call django.setup() twice:

$ ./manage.py 
Traceback (most recent call last):
  File "/home/debian/Support/django/bug-20250807/bug/lib/python3.11/site-packages/django/core/management/__init__.py", line 382, in execute
    settings.INSTALLED_APPS
...
  File "/home/debian/Support/django/bug-20250807/bug/bug/bug/__init__.py", line 9, in <module>
    django.setup()
...
  File "/home/debian/Support/django/bug-20250807/bug/bug/bad_import/models.py", line 3, in <module>
    from an_app.model import Model
ModuleNotFoundError: No module named 'an_app.model'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/debian/Support/django/bug-20250807/bug/bug/./manage.py", line 22, in <module>
    main()
...
  File "/home/debian/Support/django/bug-20250807/bug/lib/python3.11/site-packages/django/core/management/__init__.py", line 417, in execute
    django.setup()
...
  File "/home/debian/Support/django/bug-20250807/bug/lib/python3.11/site-packages/django/apps/registry.py", line 83, in populate
    raise RuntimeError("populate() isn't reentrant")
RuntimeError: populate() isn't reentrant

Best Regards,

[Jacob Walls]

Thanks for the report. The swallowing of ImportError regardless of whether it emanated from a settings module is tracked in #32915. A clear statement of the problem can also be found in #36422.