Refs #23643 -- Fixed debug view regression on Python 2.

Thanks Tomáš Ehrlich for help with the patch.

django/views/debug.py

@@ -409,7 +409,7 @@ class ExceptionReporter(object):
         # sometimes in Python 3), take the traceback from self.tb (Python 2
         # doesn't have a __traceback__ attribute on Exception)
         exc_value = exceptions.pop()
-        tb = self.tb if not exceptions else exc_value.__traceback__
+        tb = self.tb if six.PY2 or not exceptions else exc_value.__traceback__
 
         while tb is not None:
             # Support for __traceback_hide__ which is used by a few libraries
@@ -444,7 +444,9 @@ class ExceptionReporter(object):
 
             # If the traceback for current exception is consumed, try the
             # other exception.
-            if not tb.tb_next and exceptions:
+            if six.PY2:
+                tb = tb.tb_next
+            elif not tb.tb_next and exceptions:
                 exc_value = exceptions.pop()
                 tb = exc_value.__traceback__
             else:

tests/view_tests/tests/test_debug.py

@@ -14,13 +14,16 @@ from unittest import skipIf
 from django.core import mail
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.core.urlresolvers import reverse
+from django.db import DatabaseError, connection
 from django.template import TemplateDoesNotExist
 from django.test import RequestFactory, SimpleTestCase, override_settings
 from django.test.utils import LoggingCaptureMixin
 from django.utils import six
 from django.utils.encoding import force_bytes, force_text
 from django.utils.functional import SimpleLazyObject
-from django.views.debug import CallableSettingWrapper, ExceptionReporter
+from django.views.debug import (
+    CallableSettingWrapper, ExceptionReporter, technical_500_response,
+)
 
 from .. import BrokenException, except_args
 from ..views import (
@@ -194,6 +197,26 @@ class DebugViewTests(LoggingCaptureMixin, SimpleTestCase):
         )
 
 
+class DebugViewQueriesAllowedTests(SimpleTestCase):
+    # May need a query to initialize MySQL connection
+    allow_database_queries = True
+
+    def test_handle_db_exception(self):
+        """
+        Ensure the debug view works when a database exception is raised by
+        performing an invalid query and passing the exception to the debug view.
+        """
+        with connection.cursor() as cursor:
+            try:
+                cursor.execute('INVALID SQL')
+            except DatabaseError:
+                exc_info = sys.exc_info()
+
+        rf = RequestFactory()
+        response = technical_500_response(rf.get('/'), *exc_info)
+        self.assertContains(response, 'OperationalError at /', status_code=500)
+
+
 @override_settings(
     DEBUG=True,
     ROOT_URLCONF="view_tests.urls",