Setting an alias to a Django "plug-in" app

Question

Hello,

is there some pythonic way to load a django app trough an alias name? This I think would be one way to make an app more "pluggable-friendly".

there is a pattern used in settings.py:

INSTALLED_APPS = ('... ','...', )

where INSTALLED_APPS is a tuple containing names of apps. That's fine, but I don't want to put in certain apps explicitly this way.

I would like to have an app handle named say external_login_app mapping to drupal_login or mediawiki_login (to be supplied by the end user or a third party), where name of the actual custom module/app is provided by a string variable in settings.py

The pluggable part (e.g. mediawiki_login) must be a full-fledged app with it's own views, models, forms, etc, while external_login_app must be accessible anywhere in the rest of the code.

The goal here is to decouple distributed code from plugins like that.

edit 1: here is what I'm trying:

in settings.py

EXTERNAL_LOGIN = __import__(EXTERNAL_LOGIN_APP) 
#setting name must be upper case according to
#django docs

but my custom login app depends on the settings file too, so looks like I have a circular import problem with errors like module external_login does not have attribute views. This problem seems to be very insidious, as I am unable to use even simple things like render_to_response shortcut in views imported with __import__ statement in settings.py.

edit 2: after trying a while I found that using __import__() in settings.py call won't work because of almost inevitable circular dependencies

The best working method I found so far is to place __import__() calls into other .py files of the app providing the generic "consumer" interface - the one that calls the plugin functions:

in settings.py: as Michał suggests in his answer

EXTERNAL_LOGIN_APP = 'drupal_login'
INSTALLED_APPS = (
                  '...',
                  EXTERNAL_LOGIN_APP,
                )

e.g. in app/views.py:

from django.conf import settings
EXTERNAL_LOGIN = __import__(settings.EXTERNAL_LOGIN_APP, \
                            [], [], ['api','forms'])

def login_view(request, external=False):
    if external:
        form = EXTERNAL_LOGIN.forms.LoginForm(request.POST)
        if form.is_valid():
            login = form.cleaned_data['login']
            password = form.cleand_data['password']
            if EXTERNAL_LOGIN.api.check_password(login, password):
                #maybe create local account, 
                #do local authentication
                #set session cookies for the 
                #external site to synchronize logins, etc.

Answer 1

Set

LOGIN_APP_NAME = 'drupal_login' # or 'mediawiki_login', or whatever

early enough in settings.py, then put LOGIN_APP_NAME (without any quotes around it!) in your INSTALLED_APPS instead of the name of the actual app.

If you need more complex functionality involved in determining what app to use, how about putting something like external_login_app() (a function call -- put no quotes around it!) in INSTALLED_APPS and having the external_login_app function return whatever it is that it should return based on a setting in settings.py, or maybe the contents of a config file somewhere or whatever? (EDIT: Tobu's answer shows what such a function might need to return and how it might go about achieving that with __import__.)

Anyway, I'm not sure that much is achieved in this way in terms of decoupling parts of the site -- if the user still needs to modify settings.py, why not have him / her put in the name of the appropriate app in the right place? (EDIT: OK, so now I sort of see what could be gained with the right solution here... I guess the discussion continues as to how best to do what is required.)

EDIT: I posted this prior to the Original Poster amending the question with any edits, and now edit 2 includes the idea of moving the name of the login app to a separate variable in settings.py and including the variable in INSTALLED_APPS. Now that the two edits to the original question are in place, I guess I can sort of see the problem clearer, although that just makes me think that what the situation calls for is an abstract_login app with backends to support the '*_login' modules dealing with drupal, mediawiki etc. login schemes. Well, I can't say I can provide that sort of thing right now... Hope somebody else can. Will edit again should I believe I have a bright idea simplifying the whole thing beyond the OP's edits.

Answer 2

Defining the app name in settings(as Michał and your edit do) works well:

EXTERNAL_LOGIN_APP = 'drupal_login'
INSTALLED_APPS = (
                  '...',
                  EXTERNAL_LOGIN_APP,
                )

Also in settings, or in a common module, you could then factor in importing the app:

def external_login_app():
    return __import__(EXTERNAL_LOGIN_APP, …)

And use it after your imports:

external_login_app = settings.external_login_app()