Added a setup method hook for easier startup time code.

configurations/base.py

@@ -58,4 +58,6 @@ class Settings(six.with_metaclass(SettingsBase)):
     to the name of the class.
 
     """
-    pass
+    @classmethod
+    def setup(cls):
+        pass

configurations/importer.py

@@ -132,6 +132,22 @@ class SettingsImporter(object):
         return None
 
 
+def reraise(exc, prefix=None, suffix=None):
+    args = exc.args
+    if not args:
+        args = ('',)
+    if prefix is None:
+        prefix = ''
+    elif not prefix.endswith((':', ': ')):
+        prefix = prefix + ': '
+    if suffix is None:
+        suffix = ''
+    elif not (suffix.startswith('(') and suffix.endswith(')')):
+        suffix = '(' + suffix + ')'
+    exc.args = ('%s %s %s' % (prefix, exc.args[0], suffix),) + args[1:]
+    raise
+
+
 class SettingsLoader(object):
 
     def __init__(self, name, location):
@@ -143,31 +159,38 @@ class SettingsLoader(object):
             mod = sys.modules[fullname]  # pragma: no cover
         else:
             mod = imp.load_module(fullname, *self.location)
+        cls_path = '%s.%s' % (mod.__name__, self.name)
         try:
             cls = getattr(mod, self.name)
-        except AttributeError:  # pragma: no cover
-            raise ImproperlyConfigured("Couldn't find settings '%s' in "
-                                       "module '%s'" %
-                                       (self.name, mod.__package__))
+        except AttributeError as err:  # pragma: no cover
+            reraise(err,
+                    "While trying to find the '%s' settings in module '%s'" %
+                    (self.name, mod.__package__))
+        try:
+            cls.setup()
+        except Exception as err:
+            reraise(err, "While calling '%s.setup()'" % cls_path)
         try:
             obj = cls()
         except Exception as err:
-            raise ImproperlyConfigured("Couldn't load settings '%s.%s': %s" %
-                                       (mod.__name__, self.name, err))
+            reraise(err,
+                    "While loading the '%s' settings" % cls_path)
+
         try:
             attributes = uppercase_attributes(obj).items()
         except Exception as err:
-            raise ImproperlyConfigured("Couldn't get items of settings "
-                                       "'%s.%s': %s" %
-                                       (mod.__name__, self.name, err))
+            reraise(err,
+                    "While getting the items of the '%s' settings" %
+                    cls_path)
+
         for name, value in attributes:
             if callable(value) and not getattr(value, 'pristine', False):
                 try:
                     value = value()
                 except Exception as err:
-                    raise ImproperlyConfigured(
-                        "Couldn't call '%s' in '%s.%s': %s" %
-                        (value, mod.__name__, self.name, err))
+                    reraise(err,
+                            "While calling '%s.%s'" % (cls_path, value))
             setattr(mod, name, value)
+
         setattr(mod, 'CONFIGURATION', '%s.%s' % (fullname, self.name))
         return mod

configurations/tests/settings/main.py

@@ -30,6 +30,10 @@ class Test(Settings):
 
     TEST_RUNNER = 'discover_runner.DiscoverRunner'
 
+    def TEMPLATE_CONTEXT_PROCESSORS(self):
+        return Settings.TEMPLATE_CONTEXT_PROCESSORS + (
+            'configurations.tests.settings.base.test_callback',)
+
     ATTRIBUTE_SETTING = True
 
     _PRIVATE_SETTING = 'ryan'
@@ -49,6 +53,6 @@ class Test(Settings):
     def PRISTINE_FUNCTION_SETTING():
         return 5
 
-    def TEMPLATE_CONTEXT_PROCESSORS(self):
-        return Settings.TEMPLATE_CONTEXT_PROCESSORS + (
-            'configurations.tests.settings.base.test_callback',)
+    @classmethod
+    def setup(cls):
+        cls.SETUP_TEST_SETTING = 6

configurations/tests/test_main.py

@@ -25,6 +25,7 @@ class MainTests(TestCase):
                          global_settings.TEMPLATE_CONTEXT_PROCESSORS + (
                              'configurations.tests.settings.base.test_callback',
                          ))
+        self.assertEqual(main.SETUP_TEST_SETTING, 6)
 
     def test_global_arrival(self):
         from django.conf import settings
@@ -34,6 +35,7 @@ class MainTests(TestCase):
         self.assertTrue(lambda: callable(settings.PRISTINE_LAMBDA_SETTING))
         self.assertNotEqual(settings.PRISTINE_FUNCTION_SETTING, 5)
         self.assertTrue(lambda: callable(settings.PRISTINE_FUNCTION_SETTING))
+        self.assertEqual(settings.SETUP_TEST_SETTING, 6)
 
     @patch.dict(os.environ, clear=True, DJANGO_CONFIGURATION='Test')
     def test_empty_module_var(self):

docs/index.rst

@@ -155,6 +155,36 @@ Lambdas work, too::
     class Prod(Settings):
         ACCESS_FUNCTION = pristine(lamda user: user.is_staff)
 
+Setup methods
+^^^^^^^^^^^^^
+
+.. versionadded:: 0.3
+
+If there is something required to be set up after all the settings have been
+loaded please override the ``setup`` class method like so (don't forget
+to apply the Python ``@classmethod`` decorator::
+
+    from configurations import Settings
+
+    class Prod(Settings):
+        # ...
+
+        @classmethod
+        def setup(cls):
+            if something.completely.different():
+                cls.DEBUG = True
+
+Or do something unrelated to your settings, like connecting to a database::
+
+    from configurations import Settings
+
+    class Prod(Settings):
+        # ...
+
+        @classmethod
+        def setup(cls):
+            import mango
+            mango.connect('enterprise')
 
 Alternatives
 ------------