Fix duplicated database queries for paginated lists.

Closes #713.

docs/topics/release-notes.md

@@ -48,6 +48,7 @@ You can determine your currently installed version using `pip freeze`:
 * Filtering backends are now applied to the querysets for object lookups as well as lists.  (Eg you can use a filtering backend to control which objects should 404)
 * Deal with error data nicely when deserializing lists of objects.
 * Extra override hook to configure `DjangoModelPermissions` for unauthenticated users.
+* Bugfix: Fix regression which caused extra database query on paginated list views.
 * Bugfix: Fix pk relationship bug for some types of 1-to-1 relations.
 * Bugfix: Workaround for Django bug causing case where `Authtoken` could be registered for cascade delete from `User` even if not installed.
 

rest_framework/fields.py

@@ -26,14 +26,16 @@ def is_simple_callable(obj):
     """
     True if the object is a callable that takes no arguments.
     """
-    try:
-        args, _, _, defaults = inspect.getargspec(obj)
-    except TypeError:
+    function = inspect.isfunction(obj)
+    method = inspect.ismethod(obj)
+
+    if not (function or method):
         return False
-    else:
-        len_args = len(args) if inspect.isfunction(obj) else len(args) - 1
-        len_defaults = len(defaults) if defaults else 0
-        return len_args <= len_defaults
+
+    args, _, _, defaults = inspect.getargspec(obj)
+    len_args = len(args) if function else len(args) - 1
+    len_defaults = len(defaults) if defaults else 0
+    return len_args <= len_defaults
 
 
 def get_component(obj, attr_name):

rest_framework/tests/pagination.py

@@ -73,7 +73,9 @@ class IntegrationTestPagination(TestCase):
         GET requests to paginated ListCreateAPIView should return paginated results.
         """
         request = factory.get('/')
-        response = self.view(request).render()
+        # Note: Database queries are a `SELECT COUNT`, and `SELECT <fields>`
+        with self.assertNumQueries(2):
+            response = self.view(request).render()
         self.assertEqual(response.status_code, status.HTTP_200_OK)
         self.assertEqual(response.data['count'], 26)
         self.assertEqual(response.data['results'], self.data[:10])
@@ -81,7 +83,8 @@ class IntegrationTestPagination(TestCase):
         self.assertEqual(response.data['previous'], None)
 
         request = factory.get(response.data['next'])
-        response = self.view(request).render()
+        with self.assertNumQueries(2):
+            response = self.view(request).render()
         self.assertEqual(response.status_code, status.HTTP_200_OK)
         self.assertEqual(response.data['count'], 26)
         self.assertEqual(response.data['results'], self.data[10:20])
@@ -89,7 +92,8 @@ class IntegrationTestPagination(TestCase):
         self.assertNotEqual(response.data['previous'], None)
 
         request = factory.get(response.data['next'])
-        response = self.view(request).render()
+        with self.assertNumQueries(2):
+            response = self.view(request).render()
         self.assertEqual(response.status_code, status.HTTP_200_OK)
         self.assertEqual(response.data['count'], 26)
         self.assertEqual(response.data['results'], self.data[20:])