Duplicates apps in settings.INSTALLED_APPS

[trbs]

Duplicated in settings.INSTALLED_APPS are not removed automaticly.

As my project grows and the application lists grows with it, i tent to split of parts into a different python project
which i include in every django site i build. For the settings.py of the website it includes all the defaults from myproject.conf.settings
but this sometimes leads to duplicated in the INSTALLED_APPS list.

The duplicates are a human error and should not happen (or be avoided) but that doesn't mean it won't happen someday (specially with different developers working at the same site).

Attached to this ticket is a patch to check for duplicates while creating the django settings object in django.conf.init
I think that while developers should not put duplicates in there list, checking it while looping through DJANGO_SETTINGS_MODULE.INSTALLED_APPS and handling it explicitly is a good idea. (zen: Explicit is better then implicit)

The implementation currently uses a Set object, but could also be written with an
condition:

...
          if not app in new_installed_apps:
              new_installed_apps.append(app)
...

Would love to hear some comments on this :-)

As i think currently this is not checked/handled at all, the list just contains duplicate entries and that
could break some things, like registration in newformsadmin or databrowse.

Personally i believe it should check and either automaticly remove duplicates or raise some exception indicating
that duplicate values are not allowed.

[Jacob]

Nah, cleaning up for sloppy programmers isn't something Django should do. Don't put duplicates in INSTALLED_APPS.

[trbs]

Jacob, then why not raise an exception when a duplicate is found ?

Like said in the ticket, i also feel that Django should not cleanup after sloppy programmers, but it would be nice if it would be checked.
The thought was that bailing out with a DuplicateInstalledAppsError would be much clearer then continuing and getting a deeper error raised which may not always be obviously pointing to the duplicate apps in the list.

Anyways thanks as always for the great work you guys do :)

[Jacob]

Replying to trbs:

Jacob, then why not raise an exception when a duplicate is found ?

That's not a bad idea per se, but if we added checks for every possible mistake a programmer could make we'd be here all day. I'd rather just rely on folks being generally smart enough not to do things that don't work.