Move to PEP-451 style loader

configurations/importer.py

@@ -1,4 +1,3 @@
-import importlib.util
 from importlib.machinery import PathFinder
 import logging
 import os
@@ -47,12 +46,12 @@ def create_parser(self, prog_name, subcommand):
             return parser
 
         base.BaseCommand.create_parser = create_parser
-        importer = ConfigurationImporter(check_options=check_options)
+        importer = ConfigurationFinder(check_options=check_options)
         sys.meta_path.insert(0, importer)
         installed = True
 
 
-class ConfigurationImporter:
+class ConfigurationFinder(PathFinder):
     modvar = SETTINGS_ENVIRONMENT_VARIABLE
     namevar = CONFIGURATION_ENVIRONMENT_VARIABLE
     error_msg = ("Configuration cannot be imported, "
@@ -71,7 +70,7 @@ def __init__(self, check_options=False):
             self.announce()
 
     def __repr__(self):
-        return "<ConfigurationImporter for '{}.{}'>".format(self.module,
+        return "<ConfigurationFinder for '{}.{}'>".format(self.module,
                                                               self.name)
 
     @property
@@ -129,56 +128,53 @@ def stylize(text):
 
     def find_spec(self, fullname, path=None, target=None):
         if fullname is not None and fullname == self.module:
-            spec = PathFinder.find_spec(fullname, path)
+            spec = super().find_spec(fullname, path, target)
             if spec is not None:
-                return importlib.machinery.ModuleSpec(spec.name,
-                    ConfigurationLoader(self.name, spec),
-                    origin=spec.origin)
-        return None
-
-
-class ConfigurationLoader:
-
-    def __init__(self, name, spec):
-        self.name = name
-        self.spec = spec
-
-    def load_module(self, fullname):
-        if fullname in sys.modules:
-            mod = sys.modules[fullname]  # pragma: no cover
+                wrap_loader(spec.loader, self.name)
+                return spec
         else:
-            mod = importlib.util.module_from_spec(self.spec)
-            sys.modules[fullname] = mod
-            self.spec.loader.exec_module(mod)
-
-        cls_path = f'{mod.__name__}.{self.name}'
-
-        try:
-            cls = getattr(mod, self.name)
-        except AttributeError as err:  # pragma: no cover
-            reraise(err, "Couldn't find configuration '{}' "
-                         "in module '{}'".format(self.name,
-                                                  mod.__package__))
-        try:
-            cls.pre_setup()
-            cls.setup()
-            obj = cls()
-            attributes = uppercase_attributes(obj).items()
-            for name, value in attributes:
-                if callable(value) and not getattr(value, 'pristine', False):
-                    value = value()
-                    # in case a method returns a Value instance we have
-                    # to do the same as the Configuration.setup method
-                    if isinstance(value, Value):
-                        setup_value(mod, name, value)
-                        continue
-                setattr(mod, name, value)
-
-            setattr(mod, 'CONFIGURATION', '{}.{}'.format(fullname,
-                                                           self.name))
-            cls.post_setup()
-
-        except Exception as err:
-            reraise(err, f"Couldn't setup configuration '{cls_path}'")
-
-        return mod
+            return None
+
+
+def wrap_loader(loader, class_name):
+    class ConfigurationLoader(loader.__class__):
+        def exec_module(self, module):
+            super().exec_module(module)
+
+            mod = module
+
+            cls_path = f'{mod.__name__}.{class_name}'
+
+            try:
+                cls = getattr(mod, class_name)
+            except AttributeError as err:  # pragma: no cover
+                reraise(
+                    err,
+                    (
+                        f"Couldn't find configuration '{class_name}' in "
+                        f"module '{mod.__package__}'"
+                    ),
+                )
+            try:
+                cls.pre_setup()
+                cls.setup()
+                obj = cls()
+                attributes = uppercase_attributes(obj).items()
+                for name, value in attributes:
+                    if callable(value) and not getattr(value, 'pristine', False):
+                        value = value()
+                        # in case a method returns a Value instance we have
+                        # to do the same as the Configuration.setup method
+                        if isinstance(value, Value):
+                            setup_value(mod, name, value)
+                            continue
+                    setattr(mod, name, value)
+
+                setattr(mod, 'CONFIGURATION', '{0}.{1}'.format(module.__name__,
+                                                               class_name))
+                cls.post_setup()
+
+            except Exception as err:
+                reraise(err, "Couldn't setup configuration '{0}'".format(cls_path))
+
+    loader.__class__ = ConfigurationLoader

tests/test_main.py

@@ -7,7 +7,7 @@
 
 from unittest.mock import patch
 
-from configurations.importer import ConfigurationImporter
+from configurations.importer import ConfigurationFinder
 
 ROOT_DIR = os.path.dirname(os.path.dirname(__file__))
 TEST_PROJECT_DIR = os.path.join(ROOT_DIR, 'test_project')
@@ -42,12 +42,14 @@ def test_global_arrival(self):
 
     @patch.dict(os.environ, clear=True, DJANGO_CONFIGURATION='Test')
     def test_empty_module_var(self):
-        self.assertRaises(ImproperlyConfigured, ConfigurationImporter)
+        with self.assertRaises(ImproperlyConfigured):
+            ConfigurationFinder()
 
     @patch.dict(os.environ, clear=True,
                 DJANGO_SETTINGS_MODULE='tests.settings.main')
     def test_empty_class_var(self):
-        self.assertRaises(ImproperlyConfigured, ConfigurationImporter)
+        with self.assertRaises(ImproperlyConfigured):
+            ConfigurationFinder()
 
     def test_global_settings(self):
         from configurations.base import Configuration
@@ -70,21 +72,21 @@ def test_repr(self):
                 DJANGO_SETTINGS_MODULE='tests.settings.main',
                 DJANGO_CONFIGURATION='Test')
     def test_initialization(self):
-        importer = ConfigurationImporter()
-        self.assertEqual(importer.module, 'tests.settings.main')
-        self.assertEqual(importer.name, 'Test')
+        finder = ConfigurationFinder()
+        self.assertEqual(finder.module, 'tests.settings.main')
+        self.assertEqual(finder.name, 'Test')
         self.assertEqual(
-            repr(importer),
-            "<ConfigurationImporter for 'tests.settings.main.Test'>")
+            repr(finder),
+            "<ConfigurationFinder for 'tests.settings.main.Test'>")
 
     @patch.dict(os.environ, clear=True,
                 DJANGO_SETTINGS_MODULE='tests.settings.inheritance',
                 DJANGO_CONFIGURATION='Inheritance')
     def test_initialization_inheritance(self):
-        importer = ConfigurationImporter()
-        self.assertEqual(importer.module,
+        finder = ConfigurationFinder()
+        self.assertEqual(finder.module,
                          'tests.settings.inheritance')
-        self.assertEqual(importer.name, 'Inheritance')
+        self.assertEqual(finder.name, 'Inheritance')
 
     @patch.dict(os.environ, clear=True,
                 DJANGO_SETTINGS_MODULE='tests.settings.main',
@@ -93,12 +95,12 @@ def test_initialization_inheritance(self):
                                 '--settings=tests.settings.main',
                                 '--configuration=Test'])
     def test_configuration_option(self):
-        importer = ConfigurationImporter(check_options=False)
-        self.assertEqual(importer.module, 'tests.settings.main')
-        self.assertEqual(importer.name, 'NonExisting')
-        importer = ConfigurationImporter(check_options=True)
-        self.assertEqual(importer.module, 'tests.settings.main')
-        self.assertEqual(importer.name, 'Test')
+        finder = ConfigurationFinder(check_options=False)
+        self.assertEqual(finder.module, 'tests.settings.main')
+        self.assertEqual(finder.name, 'NonExisting')
+        finder = ConfigurationFinder(check_options=True)
+        self.assertEqual(finder.module, 'tests.settings.main')
+        self.assertEqual(finder.name, 'Test')
 
     def test_configuration_argument_in_cli(self):
         """