Be more informative when reporting import errors.

rest_framework/settings.py

@@ -115,8 +115,8 @@ def import_from_string(val, setting_name):
         module_path, class_name = '.'.join(parts[:-1]), parts[-1]
         module = importlib.import_module(module_path)
         return getattr(module, class_name)
-    except:
-        msg = "Could not import '%s' for API setting '%s'" % (val, setting_name)
+    except ImportError as e:
+        msg = "Could not import '%s' for API setting '%s'. %s: %s." % (val, setting_name, e.__class__.__name__, e)
         raise ImportError(msg)
 
 

rest_framework/tests/extras/bad_import.py

+raise ValueError

rest_framework/tests/settings.py

+"""Tests for the settings module"""
+from django.test import TestCase
+
+from rest_framework.settings import APISettings, DEFAULTS, IMPORT_STRINGS
+
+
+class TestSettings(TestCase):
+    """Tests relating to the api settings"""
+
+    def test_non_import_errors(self):
+        """Make sure other errors aren't suppressed."""
+        settings = APISettings({'DEFAULT_MODEL_SERIALIZER_CLASS': 'rest_framework.tests.extras.bad_import.ModelSerializer'}, DEFAULTS, IMPORT_STRINGS)
+        with self.assertRaises(ValueError):
+            settings.DEFAULT_MODEL_SERIALIZER_CLASS
+
+    def test_import_error_message_maintained(self):
+        """Make sure real import errors are captured and raised sensibly."""
+        settings = APISettings({'DEFAULT_MODEL_SERIALIZER_CLASS': 'rest_framework.tests.extras.not_here.ModelSerializer'}, DEFAULTS, IMPORT_STRINGS)
+        with self.assertRaises(ImportError) as cm:
+            settings.DEFAULT_MODEL_SERIALIZER_CLASS
+        self.assertTrue('ImportError' in str(cm.exception))