Django 1.10: Url pattern doesn't use _callback_str.

Fixes #3941

tools/test-backend

@@ -84,7 +84,6 @@ not_yet_fully_covered = {
     # they don't!  There are open issues for all of these.
     'zerver/tests/test_narrow.py',
     'zerver/tests/test_tornado.py',
-    'zerver/tests/test_urls.py',
     # Getting views file coverage to 100% is a major project goal
     'zerver/views/auth.py',
     'zerver/views/home.py',

zerver/tests/test_urls.py

@@ -9,7 +9,7 @@ import ujson
 
 import django.core.urlresolvers
 from django.test import TestCase
-from typing import List
+from typing import List, Optional
 
 from zerver.lib.test_classes import ZulipTestCase
 from zerver.models import Stream
@@ -108,6 +108,12 @@ class PublicURLTest(ZulipTestCase):
             self.assertEqual('ABCD', data['google_client_id'])
 
 class URLResolutionTest(TestCase):
+    def get_callback_string(self, pattern):
+        # type: (django.core.urlresolvers.RegexURLPattern) -> Optional[str]
+        callback_str = hasattr(pattern, 'lookup_str') and 'lookup_str'
+        callback_str = callback_str or '_callback_str'
+        return getattr(pattern, callback_str, None)
+
     def check_function_exists(self, module_name, view):
         # type: (str, str) -> None
         module = importlib.import_module(module_name)
@@ -117,9 +123,8 @@ class URLResolutionTest(TestCase):
     def test_rest_api_url_resolution(self):
         # type: () -> None
         for pattern in urls.v1_api_and_json_patterns:
-            if not (hasattr(pattern, "_callback_str") and hasattr(pattern, "default_args")):
-                continue
-
+            callback_str = self.get_callback_string(pattern)
+            if callback_str and hasattr(pattern, "default_args"):
                 for func_string in pattern.default_args.values():
                     module_name, view = func_string.rsplit('.', 1)
                     self.check_function_exists(module_name, view)
@@ -130,7 +135,7 @@ class URLResolutionTest(TestCase):
     def test_non_api_url_resolution(self):
         # type: () -> None
         for pattern in urls.urlpatterns:
-            if not hasattr(pattern, "_callback_str"):
-                continue
-            (module_name, base_view) = pattern._callback_str.rsplit(".", 1)
+            callback_str = self.get_callback_string(pattern)
+            if callback_str:
+                (module_name, base_view) = callback_str.rsplit(".", 1)
                 self.check_function_exists(module_name, base_view)