"from django.db import models" clobbered in functions inside __init__.py of installed apps

[Antti Kaihola]

If an app myapp has the following __init__.py:

from django.db import models
def myfunc():
    assert models.__package__ == 'django.db.models', (
        'models is %r instead of django.db.models' % models)

then calling myapp.myfunc() throws:

AssertionError:
  models is <module 'myapp.models' from 'myapp/models.pyc'>
  instead of django.db.models

This happens only if

• myapp is in INSTALLED_APPS
• myfunc is in myapp/__init__.py, not some other module in it
• Django is r10088 or later (thanks, git bisect)

This breaks at least Satchmo from a few months back for me, probably trunk too.

r10088 claims to have fixed all dynamic imports in Django by backporting importlib from Python 2.7.

[Antti Kaihola]

a minimal test project to reproduce "models" clobbering

[Antti Kaihola]

Replying to akaihola:

Messed up the assertion error -- for myapp it's of course

AssertionError:
  models is <module 'myapp.models' from 'myapp/models.pyc'>
  instead of django.db.models

So what happens is that inside the function models points to the app's own models.py instead of django.db.models.

[Antti Kaihola]

The issue this causes in Satchmo was reported in a ​thread on the Satchmo users Google Group.

[Russell Keith-Magee]

Some extra debug: If your test case invokes

import myapp
myapp.myfunc()

or

import myapp
from myapp import model
myapp.myfunc()

everything works as expected. It's only when you run

import myapp
from myapp.models import *
myapp.myfunc()

that you get a problem.

[Aymeric Augustin]

This bug still exists in master.

After adjusting settings.py and manage.py for Django 1.6 in the test project, I was able to reproduce it:

>>> import models_clobber_test_app
>>> models_clobber_test_app.assert_models_package()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/Users/myk/Documents/dev/django/models_clobber_test_project/models_clobber_test_app/__init__.py", line 11, in assert_models_package
    'models is %r instead of django.db.models' % models)
AssertionError: models is <module 'models_clobber_test_app.models' from '/Users/myk/Documents/dev/django/models_clobber_test_project/models_clobber_test_app/models.py'> instead of django.db.models

[Aymeric Augustin]

It turns out that this has nothing to do with Django. This surprising behavior can be reproduced with plain Python modules.

% cat foo/__init__.py

bar = 42

def print_bar():
    print(bar)

% cat foo/bar.py

# Empty module.

% python

>>> from foo import print_bar
>>> print_bar()
42
>>> import foo.bar
>>> print_bar()
<module 'foo.bar' from 'foo/bar.py'>