Adding a function that filters only the available apps from a list of…

… given apps to allow for more dynamic loading behavior of an app

README.md

@@ -43,36 +43,24 @@ To register elements with the Registry you therefore need to implement the appro
 `call_function_subpath` in an app that is listed in the `INSTALLED_APPS`. The implemented function then needs to call
 the `add_item` function on the passed registry.
 
-### MultiListPartRegistry(object)
-The following functions are available:
-
-#### add_part(list, part)
-Adds the part given by the `part` parameter to the list with the name given by the `list` parameter.
-
-#### get(list)
-Returns the parts in the list with the name given by the `list` parameter. The elements are sorted before they are
-returned.
-
-#### sort_parts(parts)
-Can be overwritten to define a custom ordering of the parts. The default function simply returns the list unordered.
-
-#### load()
-When called, the class is initialized and loads the available parts into its list cache. Does nothing if the `load()`
-was already called. Is called automatically by the `get()` function. There is no need to call it explicitly unless you
-want to initialize the class before the first list is retrieved.
-
-#### reset()
-Resets the Registry to its initial state so that the parts will be reloaded the next time the `load()` function is
-called. Usually there is no need to call this as it only adds extra overhead when the parts need to be loaded again.
-
-### SingleListPartRegistry(MultiListPartRegistry)
-The following functions are additionally available:
-
-#### add_part(part)
-Adds the part given by the `part` parameter to the list.
-
-#### get()
-Returns the parts in the list. The elements are sorted before they are returned.
+To further simplify the usage of dynamic apps, the app provides a `filter_available_apps` function that filters a list
+of possible apps and returns only the ones that are available in the current installation. This allows for a highly
+dynamic configuration of django projects by allowing certain apps to be installed selectively. Use it in your
+`settings.py` to dynamically add the available apps to your `INSTALLED_APPS`
+
+#### File: settings.py
+    from django_appregistration import filter_available_apps
+    INSTALLED_APPS = [
+        'imported_app1',
+        'imported_app2',
+        'imported_app3',
+        ...
+    ] + filter_available_apps(
+        'optional_app1',
+        'optional_app2',
+        'optional_app3',
+        ...
+    )
 
 ## Example
 Here is an implementation example with a Registry implemented in the `extendable_app` app and an app `extending_app` 
@@ -107,11 +95,49 @@ The objects can be retrieved like so:
     other_parts = MyRegistry.get('other') # retrieves the `other` list
 
 
+
+##API
+
+### MultiListPartRegistry(object)
+The following functions are available:
+
+#### add_part(list, part)
+Adds the part given by the `part` parameter to the list with the name given by the `list` parameter.
+
+#### get(list)
+Returns the parts in the list with the name given by the `list` parameter. The elements are sorted before they are
+returned.
+
+#### sort_parts(parts)
+Can be overwritten to define a custom ordering of the parts. The default function simply returns the list unordered.
+
+#### load()
+When called, the class is initialized and loads the available parts into its list cache. Does nothing if the `load()`
+was already called. Is called automatically by the `get()` function. There is no need to call it explicitly unless you
+want to initialize the class before the first list is retrieved.
+
+#### reset()
+Resets the Registry to its initial state so that the parts will be reloaded the next time the `load()` function is
+called. Usually there is no need to call this as it only adds extra overhead when the parts need to be loaded again.
+
+### SingleListPartRegistry(MultiListPartRegistry)
+The following functions are additionally available:
+
+#### add_part(part)
+Adds the part given by the `part` parameter to the list.
+
+#### get()
+Returns the parts in the list. The elements are sorted before they are returned.
+
+
 ##Running the tests
 
 The included tests can be run standalone by running the `tests/runtests.py` script. You need to have Django and
 mock installed for them to run. If you also want to run coverage, you need to install it before running the tests
 
+###v.0.0.4
+- Adding the `filter_available_apps` function that checks a list of given apps for their availability.
+
 ###v.0.0.3
 - Bugfix: Also moved the `lock` and the `loaded` attributes into the meta class 
 
@@ -128,4 +154,4 @@ used the same list resulting in element mixtures if more than one registry was u
 
 
 ## Maintainers
-This Project is maintaned by [Northbridge Development Konrad & Schneider GbR](http://www.northbridge-development.de) Softwareentwicklung
+This Project is maintained by [Northbridge Development Konrad & Schneider GbR](http://www.northbridge-development.de) Softwareentwicklung.

django_appregistration/__init__.py

@@ -4,6 +4,7 @@
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.encoding import force_text
+import imp
 from six import with_metaclass
 
 __author__ = 'Tim Schneider <tim.schneider@northbridge-development.de>'
@@ -82,4 +83,21 @@ def add_part(cls, part):
 
     @classmethod
     def get(cls):
-        return super(SingleListPartRegistry, cls).get('')
+        return super(SingleListPartRegistry, cls).get('')
+
+
+def filter_available_apps(*app_list):
+    '''
+    Checks for the availability of the given apps and returns a list with only the available apps
+    :param app_list: The list of the candidate apps to check for
+    :return: The list of apps from the candidate list that are actually available
+    '''
+
+    available_apps = []
+    for app in app_list:
+        try:
+            imp.find_module(app)
+            available_apps.append(app)
+        except ImportError:
+            pass
+    return available_apps

django_appregistration/tests/test___init__.py

@@ -5,7 +5,7 @@
 
 from django.test import TestCase
 from mock import patch, MagicMock
-from django_appregistration import MultiListPartRegistry, SingleListPartRegistry
+from django_appregistration import MultiListPartRegistry, SingleListPartRegistry, filter_available_apps
 
 try:
     from django.test import override_settings
@@ -198,3 +198,21 @@ class Registry2(SingleListPartRegistry):
 
         self.assertEqual(len(Registry1.get()), 1)
         self.assertEqual(len(Registry2.get()), 1)
+
+
+class FilterAvailableAppsTestCase(TestCase):
+    def test_filter_available_apps_list(self):
+        test_apps = (
+            'django',
+            'non_existent',
+            'django_appregistration',
+        )
+        desired_result = [
+            'django',
+            'django_appregistration',
+        ]
+
+        self.assertListEqual(
+            desired_result,
+            filter_available_apps(*test_apps)
+        )

setup.py

@@ -23,7 +23,7 @@
 
 setup(
     name='django-appregistration',
-    version='0.0.3',
+    version='0.0.4',
     packages=find_packages(exclude=['*.tests',]),
     include_package_data=True,
     install_requires=['Django >=1.6',],