Empty migrations dir causes exception

[lhn@…]

]$ python manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: admin, auth, contenttypes, sessions
  Apply all migrations: (none)
Synchronizing apps without migrations:
  Creating tables...
  Installing custom SQL...
  Installing indexes...
Installed 0 object(s) from 0 fixture(s)
Running migrations:
  No migrations needed.
Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/core/management/__init__.py", line 427, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/core/management/__init__.py", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/core/management/base.py", line 337, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/core/management/commands/migrate.py", line 140, in handle
    changes = autodetector.changes(graph=executor.loader.graph)
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/db/migrations/autodetector.py", line 34, in changes
    changes = self._arrange_for_graph(changes, graph)
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/db/migrations/autodetector.py", line 312, in _arrange_for_graph
    if app_leaf is None and not self.questioner.ask_initial(app_label):
  File "/usr/lib/python3.3/site-packages/Django-1.7a1-py3.3.egg/django/db/migrations/questioner.py", line 42, in ask_initial
    filenames = os.listdir(os.path.dirname(migrations_module.__file__))
AttributeError: 'module' object has no attribute '__file__'

Note: I'm using python3, not tested on python2

After deleting db.sqlite3 and all files in wishes/migrations and got the error above, when running migrate.
Deleting the same, plus the migrations directory solved the problem.

[Markus Holtermann]

This happens if the directory exists but does not contain a __init__.py file

[Carl Meyer]

This happens because in Python 3.3+, __init__.py is not required; a package without one is considered a namespace package (see ​PEP 420). Namespace packages do not have a __file__ attribute (it is not actually a required attribute for Python packages); they do have a __path__ attribute (which is a required attribute, and may potentially have more than one path on it).

See #17304 and #21862, and see ​https://github.com/django/django/pull/2212 for the approach app-loading is taking to this issue.

I think it would be best if migrations did not rely on __file__ but used __path__ instead. It could check if len(migrations_module.__path__) > 1 and raise an error in that case, like app-loading will.

[Andrew Godwin <andrew@…>]

In 935e6c1dfc10808272bfda1bbda03bfee035f3dc:

Fixed #21868: Don't die when seeing py3 namespace packages for mig dirs