Make utils.local_import check INSTALLED_APPS for compound paths

 - Checks all possible iterations of app name against `INSTALLED_APPS`, so `app.sub_app.module.Class` checks `INSTALLED_APPS` for `app.sub_app.module`, then `app.sub_app`, then `app`, instead of just checking for `app`.

 - Adds test to characterize new import behavior.

 - Fixes issue evenicoulddoit#13

rest_framework_serializer_extensions/utils.py

@@ -15,9 +15,14 @@ def import_local(path_to_object):
     """
     path, name = path_to_object.rsplit('.', 1)
 
-    app = path.split('.')[0]
-
-    if app not in settings.INSTALLED_APPS:
+    path_pieces = path.split('.')
+    while path_pieces:
+        if '.'.join(path_pieces) not in settings.INSTALLED_APPS:
+            path_pieces.pop()
+        else:
+            break
+
+    if not path_pieces:
         raise AssertionError(
             "Cannot import from outside installed apps"
         )

test_package/test_module/serializers.py

@@ -0,0 +1,2 @@
+class TestSerializer(object):
+    pass

tests/conftest.py

@@ -34,6 +34,7 @@ def pytest_configure():
             'rest_framework.authtoken',
             'rest_framework_serializer_extensions',
             'tests',
+            'test_package.test_module',
         ),
         PASSWORD_HASHERS=(
             'django.contrib.auth.hashers.SHA1PasswordHasher',

tests/test_utils.py

@@ -4,6 +4,7 @@
 from django.test import override_settings, TestCase
 
 from rest_framework_serializer_extensions import fields, utils
+from test_package.test_module.serializers import TestSerializer
 from tests import models
 from tests.base import TEST_HASH_IDS
 
@@ -30,6 +31,12 @@ def test_import_within_installed_apps(self):
         )
         self.assertIs(imported, fields.HashIdField)
 
+    def test_import_complex_path_within_installed_apps(self):
+        imported = utils.import_local(
+            'test_package.test_module.serializers.TestSerializer'
+        )
+        self.assertIs(imported, TestSerializer)
+
 
 class GetSettingTests(TestCase):
     """