Autodiscovery

Warning

This is just a stub document. It will be fleshed out more.

What problem does this pattern solve?

An app provides a service that requires complex configuration or customization by other apps to properly use it.

When to use it

Why should I use it?

Implementation

For each app, we need to look for an specific module inside that app’s package. We can’t use os.path here – recall that modules may be imported different ways (think zip files) – so we need to get the app’s __path__ and look for the module on that path.

Step 1: find out the app’s __path__ Import errors here will (and should) bubble up, but a missing __path__ (which is legal, but weird) fails silently – apps that do weird things with __path__ might need to roll their own index registration.

Step 2: use imp.find_module to find the app’s search_indexes.py. For some reason imp.find_module raises ImportError if the app can’t be found but doesn’t actually try to import the module. So skip this app if its search_indexes.py doesn’t exist

Step 3: import the app’s search_index file. If this has errors we want them to bubble up.

Django Snippet 2404: Generic Autodiscovery

def generic_autodiscover(module_name):
    """
    Usage:
        generic_autodiscover('commands') <-- find all commands.py and load 'em
    """
    import imp
    from django.conf import settings
    
    for app in settings.INSTALLED_APPS:
        try:
            import_module(app)
            app_path = sys.modules[app].__path__
        except AttributeError:
            continue
        try:
            imp.find_module(module_name, app_path)
        except ImportError:
            continue
        import_module('%s.%s' % (app, module_name))
        app_path = sys.modules['%s.%s' % (app, module_name)]

How to use it

Sources

Useful Links

• Generic Autodiscovery
• Looking at registration patterns in Django
• django-config-wizard autodiscover.py

Where is it used?