[1.5.x] Fixed #20278 -- ensured .get() exceptions do not recurse infinitely

A regression caused by d5b93d3281 made .get() error
reporting recurse infinitely on certain rare conditions. Fixed this by
not trying to print the given lookup kwargs.

Backpatch of 266c0bb23e

tests/modeltests/basic/tests.py

@@ -8,7 +8,7 @@ from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
 from django.utils import six
 from django.utils.translation import ugettext_lazy
 
-from .models import Article
+from .models import Article, SelfRef
 
 
 class ModelTest(TestCase):
@@ -84,23 +84,14 @@ class ModelTest(TestCase):
         # parameters don't match any object.
         six.assertRaisesRegex(self,
             ObjectDoesNotExist,
-            "Article matching query does not exist. Lookup parameters were "
-            "{'id__exact': 2000}",
+            "Article matching query does not exist.",
             Article.objects.get,
             id__exact=2000,
         )
         # To avoid dict-ordering related errors check only one lookup
         # in single assert.
-        six.assertRaisesRegex(self,
+        self.assertRaises(
             ObjectDoesNotExist,
-            ".*'pub_date__year': 2005.*",
-            Article.objects.get,
-            pub_date__year=2005,
-            pub_date__month=8,
-        )
-        six.assertRaisesRegex(self,
-            ObjectDoesNotExist,
-            ".*'pub_date__month': 8.*",
             Article.objects.get,
             pub_date__year=2005,
             pub_date__month=8,
@@ -108,8 +99,7 @@ class ModelTest(TestCase):
 
         six.assertRaisesRegex(self,
             ObjectDoesNotExist,
-            "Article matching query does not exist. Lookup parameters were "
-            "{'pub_date__week_day': 6}",
+            "Article matching query does not exist.",
             Article.objects.get,
             pub_date__week_day=6,
         )
@@ -639,3 +629,8 @@ class ModelTest(TestCase):
         Article.objects.bulk_create([Article(headline=lazy, pub_date=datetime.now())])
         article = Article.objects.get()
         self.assertEqual(article.headline, notlazy)
+
+    def test_ticket_20278(self):
+        sr = SelfRef.objects.create()
+        with self.assertRaises(ObjectDoesNotExist):
+            SelfRef.objects.get(selfref=sr)